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What was the outcome of Rutherford's alpha-particle scattering experiment? | Rutherford's alpha-particle scattering experiment led to the discovery of the atomic nucleus. He found that alpha particles were deflected from their path, indicating the presence of a small, dense nucleus at the center of the atom. | easy | qa_0001 | 64 | 58 | Grade 9 |
How do electrons contribute to the stability of an atom according to Neils Bohr's model? | According to Neils Bohr's model, electrons are distributed in different shells with discrete energy around the nucleus. If the atomic shells are complete, then the atom will be stable and less reactive. This means that when all the energy levels in an atom are occupied, the atom is more stable and tends to lose its rea... | medium | qa_0002 | 64 | 58 | Grade 9 |
What are the three sub-atomic particles of an atom, and what are their properties? | The three sub-atomic particles of an atom are electrons, protons, and neutrons. Electrons are negatively charged, protons are positively charged, and neutrons have no charge. Additionally, the mass of an electron is about 1/2000 that of a hydrogen atom, while the mass of a proton and a neutron is taken as one unit each... | easy | qa_0003 | 64 | 58 | Grade 9 |
Why does the sound of thunder take some time to reach you after you see the lightning? | This happens because light travels much faster than sound. When you see lightning, it means the light from the lightning has already reached you. However, the sound of thunder takes some time to reach you because sound travels at a slower speed than light. This is why you see the lightning before you hear the thunder. | easy | qa_0004 | 112 | 105 | Grade 9 |
How can you calculate the distance of the nearest point of lightning if you know the speed of sound in air? | To calculate the distance of the nearest point of lightning, you need to measure the time interval between seeing the lightning and hearing the thunder. Using the speed of sound in air (346 m/s), you can calculate the distance by multiplying the time interval by the speed of sound. | medium | qa_0005 | 112 | 105 | Grade 9 |
What is the difference between average speed and average velocity in the context of Usha's swim? | Average speed is the total distance covered by an object divided by the total time taken. Average velocity, on the other hand, is the displacement of an object divided by the total time taken. In Usha's case, her average speed is 180 m / 60 s = 3 m/s, while her average velocity is 0 m / 60 s = 0 m/s, since she ends up ... | hard | qa_0006 | 112 | 105 | Grade 9 |
How are fish obtained in fish farms? | Fish are obtained in fish farms through various methods, including breeding and cultivating different species of fish. Fish farmers use ponds or tanks as a habitat for the fish, where they are fed with specific feed ingredients. The production capacity of the fish farm depends on various factors, such as the type of fi... | easy | qa_0007 | 223 | 216 | Grade 9 |
What are the advantages of composite fish culture? | Composite fish culture is a method where multiple species of fish are farmed together in the same pond or tank. The advantages of this method include increased production, reduced risk of disease, and improved water quality. This is because different species of fish have different feeding habits and growth rates, which... | medium | qa_0008 | 223 | 216 | Grade 9 |
Why is the value of honey affected by the pasturage of the beehive? | The value or quality of honey depends on the pasturage, or the flow, of nectar from the flowers that the bees collect. If the beehive is located near a variety of flowers, the bees will have a diverse source of nectar, resulting in a higher-quality honey. Therefore, the pasturage of the beehive directly affects the val... | medium | qa_0009 | 223 | 216 | Grade 9 |
What is the definition of an element given by Antoine Laurent Lavoisier? | Antoine Laurent Lavoisier defined an element as a basic form of matter that cannot be broken down into simpler substances by chemical reactions. | easy | qa_0010 | 35 | 29 | Grade 9 |
Why do metals show a silvery-grey or golden-yellow colour? | Metals show a silvery-grey or golden-yellow colour due to their inherent properties, which is a characteristic feature of metals. | easy | qa_0011 | 35 | 29 | Grade 9 |
How does the property of ductility in metals help us? | The property of ductility in metals allows them to be drawn into wires, making them useful for various applications such as electrical wiring, etc. | medium | qa_0012 | 35 | 29 | Grade 9 |
What is the main difference between organic farming and traditional farming? | Organic farming is a farming system that uses minimal or no chemicals, and focuses on organic manures, recycled farm wastes, and bio-agents. This approach promotes a healthier environment and ecosystem. In contrast, traditional farming relies heavily on chemical fertilizers and pesticides, which can harm the environmen... | easy | qa_0013 | 224 | 217 | Grade 9 |
How can crop yields be improved? | Crop yields can be improved through varietal improvement, which involves breeding and selecting crop varieties that are resistant to pests and diseases, have a shorter maturity period, and are more adaptable to different environments. This approach also considers factors such as good quality, biotic and abiotic resista... | medium | qa_0014 | 224 | 217 | Grade 9 |
Why is animal husbandry important? | Animal husbandry is essential for the proper care and management of farm animals, including providing shelter, feeding, breeding, and disease control. This ensures the health and well-being of the animals, and also helps to maintain a sustainable and productive farming system. By practicing good animal husbandry, farme... | medium | qa_0015 | 224 | 217 | Grade 9 |
What is the term used to describe the acceleration experienced by an object falling towards the earth? | The term used to describe the acceleration experienced by an object falling towards the earth is acceleration due to gravity, denoted by 'g'. This is the acceleration involved in an object's free fall towards the earth due to the earth's gravitational force. | easy | qa_0016 | 145 | 138 | Grade 9 |
How does the value of g get affected when an object falls far from the earth? | The value of g gets affected when an object falls far from the earth because there is a change in the magnitude of the velocity of the object. This is due to the variation in the strength of the earth's gravitational force with distance. | medium | qa_0017 | 145 | 138 | Grade 9 |
What are the values of the universal gravitational constant, mass of the earth, and radius of the earth used to calculate the value of g? | To calculate the value of g, we use the values of the universal gravitational constant (G = 6.7 × 10^-11 N m^2 kg^-2), mass of the earth (M = 6 × 10^24 kg), and radius of the earth (R). These values are used in the formula for g, which is derived from the universal law of gravitation. | medium | qa_0018 | 145 | 138 | Grade 9 |
How do the electrons in an atom get arranged in different shells? | The electrons in an atom are arranged in different shells or orbits according to the formula 2n^2, where 'n' is the orbit number or energy level index. Each shell has a specific capacity, and electrons are accommodated in a step-wise manner. This means that electrons are filled in the inner shells before moving to the ... | easy | qa_0019 | 60 | 54 | Grade 9 |
Why are electrons not accommodated in a given shell unless the inner shells are filled? | Electrons are not accommodated in a given shell unless the inner shells are filled, because electrons are filled in a step-wise manner. This ensures that the shells are not overcrowded, and the electrons are distributed evenly, following the 2n^2 formula. | easy | qa_0020 | 60 | 54 | Grade 9 |
What is the maximum number of electrons that can be accommodated in the outermost orbit of an atom? | The maximum number of electrons that can be accommodated in the outermost orbit of an atom is 8. This is the capacity of the outermost shell, and it is according to the 2n^2 formula, where n is the orbit number. | medium | qa_0021 | 60 | 54 | Grade 9 |
Why does the velocity of an object increase at a uniform rate? | The velocity of an object increases at a uniform rate because the acceleration is constant. This means that the change in velocity is the same in a given time interval, resulting in a uniform increase in velocity. | easy | qa_0022 | 118 | 111 | Grade 9 |
How can we find the distance travelled by an object if we know its initial velocity, final velocity, and time? | We can find the distance travelled by using the equation s = u t + a t^2, where s is the distance, u is the initial velocity, a is the acceleration, and t is the time. If the acceleration is uniform, then the equation simplifies to s = u t + (1/2) a t^2, but we must check the given equations in the textbook first. | medium | qa_0023 | 118 | 111 | Grade 9 |
Explain the relation between the distance travelled and the velocity-time graph shown in Fig. 8.8? | From the velocity-time graph, we can see that the distance travelled is equal to the area of the trapezium formed by the velocity-time graph. This can be mathematically represented as s = OA × OC + (AD × BD), where OA represents the initial velocity, OC represents the time interval, AD represents the change in velocity... | hard | qa_0024 | 118 | 111 | Grade 9 |
Why do antibiotics not work against viral infections? | Antibiotics do not work against viral infections because viruses use different pathways to multiply inside the host cells. This means that antibiotics, which are designed to target bacterial cell division, cannot affect viruses. As a result, taking antibiotics when we have a viral infection, such as the common cold, wi... | easy | qa_0025 | 192 | 185 | Grade 9 |
What happens when we take antibiotics for a viral infection along with a bacterial infection? | When we take antibiotics for a viral infection along with a bacterial infection, the antibiotic will only work against the bacterial part of the infection. This is because antibiotics are specifically designed to target bacterial cell division. The viral part of the infection will not be affected by the antibiotic, but... | medium | qa_0026 | 192 | 185 | Grade 9 |
Can you give an example of a disease that is caused by both a virus and a bacterium? | One example of a disease that is caused by both a virus and a bacterium is the common cold. While the common cold is usually caused by a virus, there can be secondary bacterial infections such as a sore throat or bronchitis, which can be caused by bacteria like streptococcus. In this case, antibiotics may be prescribed... | medium | qa_0027 | 192 | 185 | Grade 9 |
Why do we need to classify organisms? | We need to classify organisms to understand their complex and diverse nature in a systematic way. Classification helps us to group organisms based on their characteristics, body organisation and evolutionary relationships. This helps in easy identification, study and comparison of different species. | easy | qa_0028 | 107 | 100 | Grade 9 |
How are plants classified into different groups? | Plants are classified into five groups: Thallophytes, Bryophytes, Pteridophytes, Gymnosperms and Angiosperms. These groups are based on the increasing complexity of their body organisation, such as the presence of true roots, stems and leaves. | medium | qa_0029 | 107 | 100 | Grade 9 |
What is the binomial nomenclature and what are its components? | Binomial nomenclature is a uniform way of identification of the vast diversity of life around us. It consists of two words - a generic name and a specific name. The generic name indicates the family or group of organisms, while the specific name is unique to each species. | easy | qa_0030 | 107 | 100 | Grade 9 |
What is chromatography and how was it first used? | Chromatography is a process of separation of components of a mixture. It was first used for the separation of colours, hence the name 'chromatography' which comes from the Greek word 'kroma' meaning colour. | easy | qa_0031 | 31 | 25 | Grade 9 |
How do you set up a simple chromatography experiment? | To set up a simple chromatography experiment, draw a line on a thin strip of filter paper, put a small drop of ink at the centre of the line, and then lower the paper into a jar or beaker containing water, so that the drop of ink is just above the water level. | easy | qa_0032 | 31 | 25 | Grade 9 |
What is a possible reason for the development of newer techniques of chromatography? | The development of newer techniques of chromatography is due to the advancement in technology, allowing for more efficient and effective separation processes. | medium | qa_0033 | 31 | 25 | Grade 9 |
What is work being done on in the given situation where a girl pulls a trolley? | In the given situation, the work is being done on the trolley. The girl is applying a force to the trolley, causing it to move through a distance. So, the work being done is on the trolley. | easy | qa_0034 | 157 | 150 | Grade 9 |
Can work be done without any force acting on an object? Explain your answer with an example. | No, work cannot be done without any force acting on an object. According to the scientific concept of work, a force must be applied to an object for work to be done. An example of this is an object falling from a height due to gravity. Although a force is not applied to the object, work is still done on it as it falls ... | medium | qa_0035 | 157 | 150 | Grade 9 |
Why is it said that work is done when an object gets displaced? | Work is said to be done when an object gets displaced because it involves a change in the position of the object. When a force is applied to an object and it moves through a distance, work is done. The displacement of the object is a result of the force applied to it, and this is what constitutes work. | easy | qa_0036 | 157 | 150 | Grade 9 |
How is sound produced? | Sound is produced when there is a vibration in an object. For example, when you clap your hands, the vibration of your hands produces sound. Similarly, when you pluck a guitar string, the vibration of the string produces sound. | easy | qa_0037 | 170 | 163 | Grade 9 |
What is the law that states we can neither create nor destroy energy? | The law that states we can neither create nor destroy energy, but can only change it from one form to another, is known as the law of conservation of energy. | medium | qa_0038 | 170 | 163 | Grade 9 |
What form of energy is used to produce sound when you clap? | When you clap, the mechanical energy of your hands is converted into sound energy, which produces a sensation of hearing in our ears. | easy | qa_0039 | 170 | 163 | Grade 9 |
What is the law of conservation of energy? | The law of conservation of energy states that energy can only be converted from one form to another; it can neither be created nor destroyed. This means that the total energy before and after a transformation remains the same. | easy | qa_0040 | 164 | 157 | Grade 9 |
What happens to the total energy of a system during or after a process? | According to the law of conservation of energy, the total energy of a system remains unchanged during or after a process. Energy can only be converted from one form to another, but it cannot be created or destroyed. | easy | qa_0041 | 164 | 157 | Grade 9 |
How can we use the conservation of energy to find the height of an object? | We can use the formula for potential energy, E = mgh, where E is the potential energy, m is the mass of the object, g is the acceleration due to gravity, and h is the height of the object. By rearranging the formula to solve for h, we can find the height of the object given its potential energy and mass. | medium | qa_0042 | 164 | 157 | Grade 9 |
What is the law of gravitation that describes the force of attraction between any two objects? | The law of gravitation states that the force of attraction between any two objects is proportional to the product of their masses and inversely proportional to the square of the distance between them. This law is universal and applies to objects anywhere in the universe. | easy | qa_0043 | 153 | 146 | Grade 9 |
Why does the force of gravity decrease at higher altitudes? | The force of gravity decreases with altitude because the distance between the object and the centre of the Earth increases, which is inversely proportional to the force of gravity. As you move further away from the centre of the Earth, the gravitational force on you decreases. | medium | qa_0044 | 153 | 146 | Grade 9 |
How is the weight of a body related to its mass? | The weight of a body is equal to the product of its mass and the acceleration due to gravity. This means that the weight of an object may vary from place to place, but its mass stays constant. | easy | qa_0045 | 153 | 146 | Grade 9 |
Why does the dust come out of the carpet when it's beaten with a stick? | When a carpet is beaten with a stick, the dust particles are dislodged from the carpet fibers due to the force exerted by the stick. This is because the force applied causes the dust particles to overcome the adhesive forces holding them to the fibers, resulting in their release into the air. | easy | qa_0046 | 138 | 131 | Grade 9 |
What is the reason why the cricket ball comes to a stop after covering a short distance on a level ground? | The ball slows to a stop because there is a force on the ball opposing the motion. This force is typically friction, which acts in the opposite direction to the motion of the ball, causing it to decelerate and eventually come to rest. | medium | qa_0047 | 138 | 131 | Grade 9 |
A bus is traveling at a constant velocity. What can be concluded about the net external unbalanced force acting on it? | For an object to be traveling with a non-zero velocity, there must be a net external unbalanced force acting on it. This means that the force acting on the bus is not zero, and it is responsible for maintaining its constant velocity. The conditions for this are that the magnitude and direction of the force must be equa... | medium | qa_0048 | 138 | 131 | Grade 9 |
What is the relationship between force, mass, and acceleration as described by the second law of motion? | The second law of motion states that the force acting on an object is equal to its mass multiplied by its acceleration. This is mathematically represented as F = ma. This means that when an object's mass is greater, a greater force is required to produce a given acceleration. Similarly, when the force is greater, the a... | easy | qa_0049 | 130 | 123 | Grade 9 |
How does a fielder reduce the impact of a fast-moving cricket ball when catching it? | A fielder reduces the impact of a fast-moving cricket ball by gradually pulling his hands backwards with the ball, thereby increasing the time over which the high velocity of the ball decreases to zero. This reduces the acceleration of the ball and therefore the impact when caught. | medium | qa_0050 | 130 | 123 | Grade 9 |
What happens to an object when no net force is acting upon it? | When no net force is acting upon an object, it will continue to move with a uniform velocity. This means that the object will not change its speed or direction, and will maintain a constant velocity throughout the time period. | easy | qa_0051 | 130 | 123 | Grade 9 |
What is the condition for work to be done? | Work is said to be done when a force is acting on an object in the direction of its displacement. This is because force and displacement must be in the same direction for work to be done. | easy | qa_0052 | 159 | 152 | Grade 9 |
How is the capability of an object to do work related to energy? | An object having a capability to do work is said to possess energy. This means that the capability of an object to do work and energy are closely related concepts. | medium | qa_0053 | 159 | 152 | Grade 9 |
What is the unit of work, and what does it represent? | The unit of work is the Joule (J). One Joule is the work done when a force of 1 Newton is applied in the direction of the displacement of an object over a distance of 1 meter. It represents the energy transferred to an object when a force is applied. | hard | qa_0054 | 159 | 152 | Grade 9 |
What are the main functions of sclerenchymatous tissue in a plant? | Sclerenchymatous tissue provides strength and stiffness to the plant parts. It is also present in stems, around vascular bundles, in the veins of leaves, and in the hard covering of seeds and nuts. | easy | qa_0055 | 81 | 75 | Grade 9 |
Why are the cells of sclerenchymatous tissue dead? | The cells of sclerenchymatous tissue are dead because they have thick walls, often with no internal space inside the cell. This is because the walls are heavily thickened due to lignin. | medium | qa_0056 | 81 | 75 | Grade 9 |
Explain why sclerenchymatous tissue is found in the husk of a coconut. | Sclerenchymatous tissue is found in the husk of a coconut because it is made up of hard and stiff cells that provide strength to the plant part. The cells in this tissue are dead and have thick walls, which makes them suitable for providing protection to the coconut. | medium | qa_0057 | 81 | 75 | Grade 9 |
What is the relationship between the mass of an object and its weight on the moon? | The weight of an object on the moon is the force with which the moon attracts that object. Since the mass of the object remains the same on the earth or the moon, its weight on the moon is directly proportional to the mass of the moon and inversely proportional to the square of the radius of the moon. | easy | qa_0058 | 147 | 140 | Grade 9 |
Why does the moon exert a lesser force of attraction on objects compared to the earth? | The moon exerts a lesser force of attraction on objects because its mass is less than that of the earth. According to the universal law of gravitation, the force of attraction depends on the masses of the objects and the distance between them. | medium | qa_0059 | 147 | 140 | Grade 9 |
How is the weight of an object on the moon related to its mass on the earth? | The weight of an object on the moon is not related to its mass on the earth. The weight of an object is determined by the force of attraction between the object and the celestial body it is on (in this case, the moon), which depends on the mass of the moon and the radius of the moon, not the mass of the object on the e... | medium | qa_0060 | 147 | 140 | Grade 9 |
What is meant by the term 'Porifera' in the context of animals? | The term 'Porifera' refers to a group of organisms that have holes or 'pores' all over their body, which helps in circulating water throughout the body to bring in food and oxygen. | easy | qa_0061 | 99 | 93 | Grade 9 |
Why do animals belonging to the group Porifera have a hard outside layer or skeleton? | Animals belonging to the group Porifera have a hard outside layer or skeleton to provide support and protection to their bodies. | easy | qa_0062 | 99 | 93 | Grade 9 |
How do Porifera animals obtain food and oxygen? | Porifera animals obtain food and oxygen by circulating water throughout their bodies through a canal system, which brings in food and oxygen to the inner parts of their body. | medium | qa_0063 | 99 | 93 | Grade 9 |
What is reverberation and how can it be reduced? | Reverberation is the persistence of sound after the original sound has stopped. It can be reduced by using sound-absorbing materials like curtains, carpets, and sound-absorbing panels. These materials help to decrease the sound reflections and reduce the overall echo. | easy | qa_0064 | 185 | 178 | Grade 9 |
How does the human ear work? | The human ear works by converting sound waves into electrical signals that are then sent to the brain. It consists of the outer ear, eardrum, middle ear bones, and the cochlea. The eardrum vibrates when it receives sound waves, which are then transmitted to the cochlea through the middle ear bones, resulting in electri... | medium | qa_0065 | 185 | 178 | Grade 9 |
How can we calculate the speed of sound in water using a sonar device? | The speed of sound in water can be calculated using the time it takes for the echo to return and the distance of the object from the device. If the time taken for the echo to return is 5 seconds and the distance of the object is 3625 meters, then the speed of sound in water can be calculated using the formula: speed = ... | medium | qa_0066 | 185 | 178 | Grade 9 |
What is the unit of density? | The unit of density is kilogram per metre cube (kg m–3). This means that it is a measure of mass per unit volume of a substance. | easy | qa_0067 | 152 | 145 | Grade 9 |
Why does a body experience an upward force when it is immersed in a fluid? | A body experiences an upward force when it is immersed in a fluid because it displaces a volume of fluid that is equal in weight to the body itself. This is known as the principle of buoyancy. | medium | qa_0068 | 152 | 145 | Grade 9 |
How does the density of a substance help us determine its purity? | The density of a substance can help us determine its purity by comparing it with the known density of the same substance. If the two densities match, then the substance is likely to be pure. This is because the density of a substance remains the same under specified conditions, making it a characteristic property. | hard | qa_0069 | 152 | 145 | Grade 9 |
Why do cells need oxygen? | Cells need oxygen because it is essential for the production of energy through cellular respiration, a process that occurs in the mitochondria. During cellular respiration, oxygen acts as the final electron acceptor, allowing cells to generate ATP, which is crucial for various cellular functions. | easy | qa_0070 | 83 | 77 | Grade 9 |
How do blood and other substances move within the body? | Blood and other substances move within the body through the circulatory system, which consists of blood vessels, including arteries, veins, and capillaries. It is facilitated by the heart, which pumps blood throughout the body, and muscles, which help to propel blood forward. | medium | qa_0071 | 83 | 77 | Grade 9 |
What is the role of muscle cells in the movement of body parts? | Muscle cells, also known as muscle fibers, play a crucial role in the movement of body parts. They contract and relax to produce movement, allowing us to perform various actions, such as walking, running, and even the movement of our chest during breathing. | easy | qa_0072 | 83 | 77 | Grade 9 |
What is the outermost layer of the Earth called? | The outermost layer of the Earth is called the crust. It is the layer that contains the necessary minerals that supply nutrients to life-forms. | easy | qa_0073 | 205 | 198 | Grade 9 |
How do lichens contribute to the formation of soil? | Lichens contribute to the formation of soil by releasing certain substances while growing on the surface of rocks. These substances cause the rock surface to powder down and form a thin layer of soil. | medium | qa_0074 | 205 | 198 | Grade 9 |
What role do roots of big trees play in breaking down rocks? | The roots of big trees help in breaking down rocks further. They sometimes go into cracks in rocks, causing them to break up and contributing to the formation of soil. | medium | qa_0075 | 205 | 198 | Grade 9 |
What is the fundamental unit of matter in our surroundings? | The fundamental unit of matter in our surroundings is an atom. An atom is the smallest unit of a substance that retains the properties of the substance. It is the building block of matter and consists of protons, neutrons, and electrons. | easy | qa_0076 | 7 | 3 | Grade 9 |
What are the different types of resources that we use in our daily lives? | We use various types of natural resources in our daily lives, including living resources like animals and plants, and non-living resources like water, minerals, and fossil fuels. These resources are essential for our survival and are classified based on their renewability and sustainability. | medium | qa_0077 | 7 | 3 | Grade 9 |
What is the relationship between the structure of the atom and the properties of matter? | The structure of the atom determines the properties of matter. The arrangement of protons, neutrons, and electrons in an atom influences its chemical properties, such as reactivity and the ability to form bonds with other atoms. The structure of the atom also affects the physical properties of matter, like its density ... | hard | qa_0078 | 7 | 3 | Grade 9 |
What is the principle behind the experiment where a test tube and a cork are used to demonstrate the law of conservation of momentum? | The principle behind this experiment is the law of conservation of momentum, which states that the total momentum of a closed system remains constant, provided no external force acts on it. In this experiment, the momentum of the balls before the collision is equal to the momentum of the balls after the collision, and ... | medium | qa_0079 | 134 | 127 | Grade 9 |
Why does the test tube recoil in the direction opposite to the direction of the cork in the experiment? | The test tube recoils in the opposite direction because of the conservation of momentum. The momentum gained by the cork is equal to the momentum lost by the test tube, causing it to move in the opposite direction. | easy | qa_0080 | 134 | 127 | Grade 9 |
What is the significance of heating the test tube until water vaporises and the cork blows out in the experiment? | Heating the test tube until water vaporises and the cork blows out allows the balls inside the test tube to collide with each other, resulting in an ideal collision where the momentum is conserved. This makes it possible to observe the law of conservation of momentum in action. | medium | qa_0081 | 134 | 127 | Grade 9 |
What can be a possible effect of isolating human activities that lead to pollution to specific and limited areas? | Isolating human activities that lead to pollution to specific and limited areas might not be an effective solution to reduce pollution. This is because pollutants can still spread to other areas through air and water currents, affecting a larger region. | easy | qa_0082 | 212 | 205 | Grade 9 |
Describe how forests influence the quality of our air resources. | Forests play a crucial role in maintaining the quality of our air resources by absorbing carbon dioxide and releasing oxygen through photosynthesis. This process helps in reducing the level of carbon dioxide in the atmosphere, thus preventing the greenhouse effect and maintaining a healthy air quality. | medium | qa_0083 | 212 | 205 | Grade 9 |
Why are forests important for maintaining the quality of our soil resources? | Forests are essential for maintaining the quality of our soil resources as they help in holding the soil in place, preventing erosion, and adding organic matter to it. This leads to a fertile and healthy soil, which supports plant growth and agriculture. | medium | qa_0084 | 212 | 205 | Grade 9 |
What are the special orbits of electrons according to Bohr's model of an atom? | According to Bohr's model of an atom, only certain special orbits known as discrete orbits of electrons are allowed inside the atom. These discrete orbits are special paths that electrons can take around the nucleus of an atom. | easy | qa_0085 | 59 | 53 | Grade 9 |
Why do electrons not radiate energy while revolving in discrete orbits? | According to Bohr's model of an atom, electrons do not radiate energy while revolving in discrete orbits because they have a fixed amount of energy. This means that their motion is not random, and they do not emit energy as electromagnetic waves. | medium | qa_0086 | 59 | 53 | Grade 9 |
What would be the effect of using a metal other than gold in the α-particle scattering experiment? | The effect of using a metal other than gold in the α-particle scattering experiment would likely be a change in the scattering pattern. The amount of scattering would depend on the atomic size and density of the metal used, which would result in a different distribution of scattered α-particles. | medium | qa_0087 | 59 | 53 | Grade 9 |
What is the relationship between the mass of a substance and the number of moles of that substance? | The mass of a substance is directly proportional to the number of moles of that substance. This can be expressed as mass = molar mass × number of moles. For example, if we have 0.5 mole of nitrogen gas, and the molar mass of nitrogen is 28 g/mol, then the mass of nitrogen gas would be 14 g. | easy | qa_0088 | 52 | 46 | Grade 9 |
How do we calculate the number of particles (atoms or molecules) from the given mass of a substance? | To calculate the number of particles, we need to know the mass of the substance, the molar mass of the substance, and Avogadro's number. We can use the formula: number of particles = (given mass × Avogadro's number) / molar mass. For example, if we have 7 g of oxygen gas, with a molar mass of 32 g/mol, then we can calc... | medium | qa_0089 | 52 | 46 | Grade 9 |
Why is it essential to know Avogadro's number when dealing with the number of particles in a substance? | Avogadro's number is a constant that represents the number of particles (atoms or molecules) in one mole of a substance. It allows us to relate the number of moles of a substance to the number of particles, making it a crucial concept in chemistry. With Avogadro's number, we can easily convert between the number of mol... | medium | qa_0090 | 52 | 46 | Grade 9 |
What is the main difference between unicellular and multicellular organisms? | Unicellular organisms, like Amoeba, consist of a single cell that performs all basic functions. On the other hand, multicellular organisms have millions of cells, where most of them are specialised to carry out specific functions. | easy | qa_0091 | 78 | 72 | Grade 9 |
Why do plants need a large quantity of supportive tissue? | Plants need a large quantity of supportive tissue because they are stationary or fixed, and need to be upright to carry out their functions. This tissue is generally made up of dead cells. | easy | qa_0092 | 78 | 72 | Grade 9 |
How does the way animals consume energy differ from plants? | Animals consume more energy as compared to plants because they are constantly moving around in search of food, mates, and shelter, whereas plants are stationary and consume energy mainly through photosynthesis. | medium | qa_0093 | 78 | 72 | Grade 9 |
How do storage grain losses occur? | Storage grain losses occur due to various reasons such as rodents, insects, moisture, and fungal growth. These losses can be minimized by maintaining proper storage conditions, using rodent-proof containers, and controlling the humidity levels. | easy | qa_0094 | 225 | 218 | Grade 9 |
What is common in poultry, fisheries, and bee-keeping for increasing production? | Hybridization or selective breeding is common in poultry, fisheries, and bee-keeping for increasing production. This process involves cross-breeding different species or strains to produce offspring with desirable traits such as high yield, resistance to diseases, and improved quality. | medium | qa_0095 | 225 | 218 | Grade 9 |
How do you differentiate between capture fishing, mariculture, and aquaculture? | Capture fishing involves catching fish from natural waters, mariculture involves rearing and breeding fish in coastal waters or estuaries, and aquaculture involves cultivating fish in controlled environments such as ponds or tanks. These three methods differ in terms of their location and level of control over the envi... | hard | qa_0096 | 225 | 218 | Grade 9 |
How is sound produced by everyday objects, like a school bell? | Sound is produced when an object vibrates, causing the surrounding particles to oscillate back and forth. In the case of a school bell, it vibrates when it is struck, producing a disturbance that travels through the air particles as a longitudinal wave. This is how the sound of the bell reaches our ears. | easy | qa_0097 | 173 | 166 | Grade 9 |
Why are sound waves classified as mechanical waves? | Sound waves are classified as mechanical waves because they require a physical medium, like air, to propagate. The particles of the medium oscillate back and forth as the wave travels, which is a characteristic of mechanical waves. This distinguishes sound waves from electromagnetic waves, which can travel through a va... | medium | qa_0098 | 173 | 166 | Grade 9 |
What happens to particles in a medium when a transverse wave travels through it? | In a transverse wave, the individual particles of the medium move about their mean positions in a direction perpendicular to the direction of wave propagation. This means that the particles oscillate up and down or side to side as the wave travels, rather than moving from one place to another. | medium | qa_0099 | 173 | 166 | Grade 9 |
What is a mixture? Explain with examples. | A mixture is a physical combination of two or more substances (elements and/or compounds) in any proportion. This means that the components of a mixture can be separated from each other by physical methods. For instance, a mixture can be air which contains various gases like nitrogen, oxygen, and carbon dioxide, or a m... | easy | qa_0100 | 37 | 31 | Grade 9 |
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