datavorous/entrance-exam-dataset huggingface dataset:
The de-Broglie wavelength of a neutron in thermal equilibrium with heavy water at a temperature T (Kelvin) and mass m is:

Options:
A hmkT
B h3mkT
C 2h3mkT
D 2hmkT

The correct answer is:
h3mkT

Solution:
De-Broglie wavelength,
λ=hmv =h2mKE =h2m32kT
(Since K.E. of a thermal neutron=32kT)
⇒λ=h3mkT

Topic: Physics, Dual Nature of Matter, NEET, NEET 2017
The de-Broglie wavelength of an electron accelerated through a potential difference of 100 V is

Options:
A 12.27 â«
B 1.227 â«
C 0.1227 â«
D 0.001227 â«

The correct answer is:
1.227 â«

Solution:
De-Broglie wavelength of an electron is given by
λ=hmv=h2meV-12.27V Å
(h=Planck's constant)
Where, m=mass of electron, e=electronic charge and V=potential difference with which electron is accelerated.
λ=12.27100 Å=12.2710 Å
=1.227 Å

Topic: Physics, Dual Nature of Matter, NEET
The de-Broglie wavelength of an electron accelerated to a potential of 400 V is approximately

Options:
A 0.03 nm

B 0.04 nm

C 0.12 nm

D 0.06 nm

The correct answer is:
0.06 nm

Solution:
Voltage, V=400 V
∵ the de-Broglie wavelength of an electron
λ=12.3V A∘
=12.3400 A∘=12.320 A∘
=0.615 A∘
λ=0.0615 nm

Topic: Physics, Dual Nature of Matter, NEET
The de-Broglie wavelength of an electron in the ground state of the hydrogen atom is

Options:
A Ïr2
B 2πr
C Ïr
D 2Ïr

The correct answer is:
2πr

Solution:
According to Bohr's theroy
mvr=nh2π
2πr=nhmv
2πr=nλ
For n=1,λ=2πr

Topic: Physics, Atomic Physics, NEET
The de-Broglie wavelength of an electron moving with kinetic energy of 144 eV is nearly

Options:
A 102×10-3 nm
B 102×10-4 nm
C 102×10-5 nm
D 102×10-2 nm

The correct answer is:
102×10-3 nm

Solution:
The formula of de-Broglie wavelength, λ=h2mK.E. and we know that, K.E.=eV. Recall the proper relation between wavelength and electric potential, in angstrom, λ=12.27VÅ=12.27144×10-10=1.02×10-10 m

it means the wavelength, λ=102×10-3 nm.

Topic: Physics, Dual Nature of Matter, NEET, NEET 2020 (Phase 2)
The de-Broglie wavelength of neutrons in thermal equilibrium at temperature $T$ is:

Options:
A $\frac{3.08}{\sqrt{T}} Å$
B $\frac{0.308}{\sqrt{T}} Å$
C $\frac{0.0308}{\sqrt{T}} Å$
D $\frac{30.8}{\sqrt{T}} Å$

The correct answer is:
$\frac{30.8}{\sqrt{T}} Å$

Solution:
Using de-Broglie wavelength
$$
\begin{aligned}
\lambda & =\frac{h}{\sqrt{2 m K_B T}} \\
\lambda & =\frac{6.63 \times 10^{-34}}{\sqrt{2 \times 1.67 \times 10^{-27} \times 1.38 \times 10^{-23} \times \mathrm{T}}} \\
& =\frac{3.08 \times 10^{-34} \times 10^{25}}{\sqrt{T}} m=\frac{30.8}{\sqrt{T}} Å
\end{aligned}
$$

Topic: Physics, Dual Nature of Matter, NEET, NEET 2013 (Karnataka)
The de-Broglie wavelength of neutrons in thermal equilibrium at temperature T is

Options:
A 25.2T A∘
B 0.308T A∘
C 0.025T A∘
D 0.25T A∘

The correct answer is:
25.2T A∘

Solution:
Since, we know de-Broglie wavelength,
λ=hp
And p=2mpKE
=2mp3k2⋅T∵KE=3k2⋅T
=3mpkT
So, λ=h3mpkT
Putting the given values, we get
∴ λ=6.63×10-343×1.67×10-27×1.38×10-23×T
=2.52T×10-9 m
or λ =25.2T×10-10 m
∴ λ=25.2T A∘

Topic: Physics, Dual Nature of Matter, NEET
The declining phase of a population occurs when

Options:
A Mortality > Natality
B Natality > Mortality
C Mortality = Natality
D Natality = Mortality = 0

The correct answer is:
Mortality > Natality

Solution:
The declining population has a higher death rate than the birth rate. So the population of young members is lower than that of old members.

Topic: Biology, Organisms and Populations, NEET
The decomposition of A into product has a value of k as 4.5 × 103s–1at 10°C and energy of activation 60 kJ mol–1. At what temperature would k be 1.5 × 104s–1?

Options:
A 46°C
B 24°C
C 63°C
D 93°C

The correct answer is:
24°C

Solution:
Correct Option is : (B)
24°C

Topic: Chemistry, Chemical Kinetics, NEET
The decomposition of dimethyl ether leads to the formation of CH4,H2 and CO and the reaction rate is given by rate=kCH3OCH332

The rate of reaction is followed by increase in pressure in a closed vessel, so the rate can also be expressed in terms of the partial pressure of dimethyl ether i.e. rate=kPCH3OCH332,

If the pressure is measured in bar and time in minutes, then the unit of rate constants is:

Options:
A bar 1/2  min
B bar 3/2   min −1
C bar â1/2 â min â1
D bar min −1

The correct answer is:
bar −1/2   min −1

Solution:
As rate=kCH3OCH332
bar/min =kbar32
Unit of k=bar-12 min-1

Topic: Chemistry, Chemical Kinetics, NEET
The decomposition of dimethyl ether leads to the formation of CH4, H2and CO and the reaction rate is given by Rate = k [CH3OCH3]3/2.The rate of reaction is followed by increase in pressure in a closed vessel, so the rate can also be expressed in terms of the partial pressure of dimethyl ether, i.e., Rate = k (p(CH3OCH3))3/2If the pressure is measured in bar and time in minutes, then what are the units of rate and rate constants?

Options:
A Unit of Rate= (bar2min-2) and Unit of Rate constant=(bar−1/2min−1)
B Unit of Rate= (bar min-1) and Unit of Rate constant=(bar−1/2min−1)
C Unit of Rate= (bar min-1) and Unit of Rate constant=(bar−3/2min−1)
D Unit of Rate= (bar2min-2) and Unit of Rate constant=(bar−3/2min−1)

The correct answer is:
Unit of Rate= (bar min-1) and Unit of Rate constant=(bar−1/2min−1)

Solution:
Correct Option is : (B)
Unit of Rate= (bar min-1) and Unit of Rate constant=(bar−1/2min−1)

Topic: Chemistry, Chemical Kinetics, NEET
The decomposition of gaseous ammonia on a hot platinum surface is a reaction at high pressure is an example of which order of reaction?

Options:
A 1
B 0
C 2
D 3

The correct answer is:
0

Solution:
The decomposition of gaseous ammonia on a hot platinum surface is a reaction at high pressure is an example of zero order reaction.

Topic: Chemistry, Chemical Kinetics, NEET
The decomposition of hydrocarbon follows the equation k = (4.5 × 1011s–1) e-28000K/T.Calculate Ea.

Options:
A 465.12 kJ mol-1
B 232.79 kJ mol–1
C 836.45 kJ mol-1
D 908.33 kJ mol-1

The correct answer is:
232.79 kJ mol–1

Solution:
Correct Option is : (B)
232.79 kJ mol–1

Topic: Chemistry, Chemical Kinetics, NEET
The decomposition of N2O5in CCl4at 318K has been studied by monitoring the concentration of N2O5in the solution. Initially the concentration of N2O5is 2.33 mol L–1and after 184 minutes, it is reduced to 2.08 mol L–1. The reaction takes place according to the equation: 2N2O5(g) → 4NO2(g) + O2(g) Calculate (i) the average rate of this reaction in terms of seconds and (ii) what is the rate of production of NO2during this period?

Options:
A (i)1.13 × 10–5mol L–1s–1and (ii) 1.13 × 10–3mol L–1min–1
B (i)1.13 × 10–5mol L–1s–1and (ii) 2.72 × 10–3mol L–1min–1
C (i)2.72 × 10–5mol L–1s–1and (ii) 2.72 × 10–3mol L–1min–1
D (i)2.72 × 10–5mol L–1s–1and (ii) 1.13 × 10–3mol L–1min–1

The correct answer is:
(i)1.13 × 10–5mol L–1s–1and (ii) 2.72 × 10–3mol L–1min–1

Solution:
Correct Option is : (B)
(i)1.13 × 10–5mol L–1s–1and (ii) 2.72 × 10–3mol L–1min–1

Topic: Chemistry, Chemical Kinetics, NEET
The decomposition of NH3on the platinum surface is zero order reaction. What are the rates of production of N2and H2if k=2.5 × 10–4mol–1L s–1?

Options:
A Rate of production of N2= 7.5×10−4M/s ; Rate of production of H2= 2.5×10−4M/s
B Rate of production of N2= 2.5×10−4M/s ; Rate of production of H2= 2.5×10−4M/s
C Rate of production of N2= 7.5×10−4M/s ; Rate of production of H2= 7.5×10−4M/s
D Rate of production of N2= 2.5×10−4M/s ; Rate of production of H2= 7.5×10−4M/s

The correct answer is:
Rate of production of N2= 2.5×10−4M/s ; Rate of production of H2= 7.5×10−4M/s

Solution:
Correct Option is : (D)
Rate of production of N2= 2.5×10−4M/s ; Rate of production of H2= 7.5×10−4M/s

Topic: Chemistry, Chemical Kinetics, NEET
The decomposition of organic compounds, in the presence of oxygen and without the development of odoriferous substances, is called

Options:
A nitrification
B N2 -fixation
C decay
D denitrification

The correct answer is:
decay

Solution:
In decay reaction an organic compound is decomposed in presence of oxygen.

Topic: Chemistry, Chemical Kinetics, NEET
The decomposition of phosphine PH3 on tungsten at low pressure is a first-order reaction. It is because the

Options:
A rate is proportional to the surface coverage.
B rate is inversely proportional to the surface coverage.
C rate is independent of the surface coverage.
D rate of decomposition is very slow.

The correct answer is:
rate is proportional to the surface coverage.

Solution:
The rate is proportional to the surface coverage.
When pressure is so low that αp<<1,
Rate=krαp1+αp≈krαp.

Topic: Chemistry, Chemical Kinetics, NEET, NEET 2016 (Phase 2)
The decreasing order of boiling points of the following alkanes is:
(a) Heptane
(b) butane
(c) 2-methylbutane
(d) 2-methylpropane
(e) hexane
Choose the correct answer from the options given below:

Options:
A (a) $>$ (c) $>$ (e) $>$ (d) $>$ (b)
B (c) $>$ (d) $>$ (a) $>$ (e) $>$ (b)
C (a) $>$ (e) $>$ (b) $>$ (c) $>$ (d)
D (a) $>$ (e) $>$ (c) $>$ (b) $>$ (d)

The correct answer is:
(a) $>$ (e) $>$ (c) $>$ (b) $>$ (d)

Solution:
With increase in molecular mass, van Der Waal force increases and hence boiling point also increases.
$\therefore$ BP : Heptane \(>\) Hexane \(>\) 2- Methyl Butane \(>\) Butane \(>\) 2- methly propane with the increase in branching, surface area decreases of molecules of same molecular mass which results in decrease in boiling point.

Topic: Chemistry, Chemical Bonding and Molecular Structure, NEET, NEET 2022 (Phase 2)
The decreasing order of second ionization energy of K, Ca and Ba is

Options:
A K > Ca > Ba
B Ca > Ba > K
C Ba > K > Ca
D K > Ba > Ca

The correct answer is:
K > Ca > Ba

Solution:
The second ionization energy of K is maximum, because the second electron is removed from 3s23p6 shell. The second ionization energies of group 2 elements decrease down the group. Hence, second I.E. of Ca > second I.E. of Ba.

Topic: Chemistry, Classification of Elements and Periodicity in Properties, NEET
The decreasing order of wavelength of infrared, microwave, ultraviolet and gamma rays is

Options:
A gamma rays, ultraviolet, infrared, microwaves
B microwaves, gamma rays, infrared, ultraviolet
C infrared, microwave, ultraviolet, gamma rays
D microwave infrared, ultraviolet, gamma rays

The correct answer is:
microwave infrared, ultraviolet, gamma rays

Solution:
Decreasing order of wavelength of various rays Microwave $>$ Infrared $>$ Ultraviolet $>$ Gamma rays

Topic: Physics, Electromagnetic Waves, NEET, NEET 2011 (Screening)
The defect in Thalassemia results in ___________.

Options:
A increased rate of synthesis of one of the globin chains
B normal haemoglobin molecules
C reduced rate of synthesis of one of the globin chains
D increased rate of synthesis of all globin chains

The correct answer is:
reduced rate of synthesis of one of the globin chains

Solution:
Thalassemia is caused by a defect that results in reduced rate of synthesis of one of the globin chains (α and β chains) that make up haemoglobin, causing the formation of abnormal haemoglobin molecules.

Topic: Biology, Principles of Inheritance and Variation, NEET
The deficiencies of micronutrients, not only affects growth of plants but also vital functions such as photosynthetic and mitochondrial electron flow. Among the list given below, which group of three elements shall affect most, both photosynthetic and mitochondrial electron transport?

Options:
A $\mathrm{Co}, \mathrm{Ni}, \mathrm{Mo}$
B $\mathrm{Ca}, \mathrm{K}, \mathrm{Na}$
C $\mathrm{Mn}, \mathrm{Co}, \mathrm{Ca}$
D $\mathrm{Cu} . \mathrm{Mn}$. Fe.

The correct answer is:
$\mathrm{Cu} . \mathrm{Mn}$. Fe.

Solution:
$\mathrm{Cu}, \mathrm{Mn}$ and $\mathrm{Fe}$ Micronutrient elements affect both photosynthetic and mitochondrial electron transport as follows: Iron (Fe) - It is an important constituent of a protein involved in the transfer of electrons like ferredoxin and cytochromes. Manganese(Mn)- It activates enzymes of respiration, photosynthesis and nitrogen metabolism. Copper $(\mathrm{Cu})$ - It is a component or activator of plastocyanin, cytochrome oxidase, RuBP carboxylase.

Topic: Biology, Mineral Nutrition, NEET, NEET 2005
The deficiency of micronutrients, not only affect the growth of a plant but also affects the vital functions such as photosynthesis and cellular respiration. Among the list given below, which group of three elements shall affect both photosynthesis and cellular respiration the most?

Options:
A Cu, Mg, and Fe
B Co, Ni, and Mo
C Mn, Co, and Ca
D Ca, K, and Na

The correct answer is:
Cu, Mg, and Fe

Solution:
Copper deficiency usually results in shriveling or malformation of the leaves along with tip burn. The most easily recognized symptoms of copper deficiency are those in a disease of fruit trees called "exanthema".

Magnesium plays two very essential roles in the processes of photosynthesis and carbohydrate metabolism. Magnesium deficiencies show up as extensive chlorosis between the veins of the leaves. Chlorosis is followed by the appearance of anthocyanin pigments in the leaves such as the oranges, reds, and purples.

Iron functions in the synthesis of chloroplastic protein and thus may interfere with chlorophyll synthesis. Iron deficiencies of plant leaves appear as extensive chlorosis in the foliage.

Topic: Biology, Mineral Nutrition, NEET
The definition given below describes:

"The mass of living material at a trophic level at a particular time."

Options:
A Gross primary productivity
B Standing state
C Net primary productivity
D Standing crop

The correct answer is:
Standing crop

Solution:
Standing crop is the total amount of living material in a specified population at a particular time, generally expressed as biomass. The standing crop may show variation at different times of the year.
Net Primary Productivity (NPP) is the rate at which plants incorporate atmospheric carbon through photosynthesis. (Definition)
Gross primary production (GPP) is the rate at which an ecosystem's producers capture and store a given amount of chemical energy as biomass in a given length of time. (Definition)

Topic: Biology, Ecosystem, NEET
The definition of biotechnology, âThe integration of natural science and organisms, cells, parts thereof and molecular analogues for products and servicesâ was given by

Options:
A Genetic Engineering Approval Committee.
B European Federation of Biotechnology.
C US Patent and Trademark Office.
D International Union of Biochemistry.

The correct answer is:
European Federation of Biotechnology.

Solution:
The European Federation of Biotechnology (EFB) has given a definition of biotechnology that encompasses both traditional view and modern molecular biotechnology. The definition given by EFB is as follows ‘The integration of natural science and organisms, cells, parts thereof, and molecular analogues for products and services’.

Topic: Biology, Biotechnology - Principles and Processes, NEET
The deflection in a moving coil galvanometer is

Options:
A directly proportional to the torsional constant
B directly proportional to the number of turns in the coil
C inversely proportional to the area of the coil
D inversely proportional to the current flowing

The correct answer is:
directly proportional to the number of turns in the coil

Solution:
Deflection is directly proportional to electric current in moving coil galvanometer.
i=knBAθ⇒θ=nBAki⇒  θ∝n

Topic: Physics, Experimental Physics, NEET
The degeneracy of the genetic code allows different codons to code the same amino acid. Which of the following codons does NOT code for the simplest amino acid, glycine?

Options:
A GCU
B GGG
C GGC
D GGU

The correct answer is:
GCU

Solution:
Some amino acids are coded by more than one codon, hence the code is said to be degenerate. Glycine is the simplest amino acid with a single hydrogen atom as the R-group. 4 codons code for this amino acid - GGG, GGU, GGA, GGC.
GCU, GCC, GCA and GCG code for alanine.

Topic: Biology, Molecular Basis of Inheritance, NEET
The degree of dissociation (Î±) of a weak electrolyte, A2SO4 is related to Vant Hoff factor (i) by the expression

Options:
A i=1+2 â
B i =1+3â
C i =1+â
D i =1+4â

The correct answer is:
i=1+2 â

Solution:
A2SO4â2A+SO42-
1-â 2â â
i=1+2â
Therefore the degree of dissociation (Î±) of a weak electrolyte, A2SO4 is related to van't Hoff factor (i) by the expression i=1+2â.

Topic: Chemistry, Solutions, NEET
The degree of hardness of water is usually expressed in terms of

Options:
A g/L of CaCO3 and MgCO3 present
B ppm by weight of MgSO4
C ppm of CaCO3 actually present in water
D ppm by weight of CaCO3 irrespective of whether it is actually present

The correct answer is:
ppm by weight of CaCO3 irrespective of whether it is actually present

Solution:
The degree of hardness of water is usually expressed in terms of ppm by weight of CaCO3 irrespective of whether it is actually present.

Topic: Chemistry, s Block Elements, NEET
The degree of hydrolysis of which of the following salt is independent of the concentration of salt solution?

Options:
A CH3COONa
B CH3COONH4
C NH4Cl
D NaCl

The correct answer is:
CH3COONH4

Solution:
It is the salt of weak acid and weak base hence its degree of hydrolysis will be independent of concentration. h=KWKa×Kb

Topic: Chemistry, Ionic Equilibrium, NEET
The degree of ionization of a 0.1M bromoacetic acid solution is 0.132. Calculate the pH of the solution and the pKa of bromoacetic acid.

Options:
A pH = 1.88, pKa = 2.75
B pH = 2.45, pKa = 2.55
C pH = 2.88, pKa = 2.72
D pH = 2.45, pKa = 2.72

The correct answer is:
pH = 1.88, pKa = 2.75

Solution:
Correct Option is : (A)
pH = 1.88, pKa = 2.75

Topic: Chemistry, Ionic Equilibrium, NEET
The degree of ionization (α) of a weak electrolyte AxBy is related to van't Hoff factor by expression

Options:
A α=i-1x+y+1
B α=i-1x+y-1
C α=x+y-1i-1
D α=x+y+1i-1

The correct answer is:
α=i-1x+y-1

Solution:
α=i-1n-1
Here, n = number of ions formed = x + y
So α=i-1x+y-1 .

Topic: Chemistry, Solutions, NEET
The degrees of freedom of a molecule of a triatomic gas are

Options:
A 2
B 4
C 6
D 8

The correct answer is:
6

Solution:
As temperature requirement is not given so, the molecule of a triatomic gas has a tendency of rotating about any of three coordinate axes. So, it has 6 degrees of freedom; 3 translational and 3 rotational.
Thus,
(3 translational+3 rotational) at room temperature.

Topic: Physics, Kinetic Theory of Gases, NEET
The d-electron configurations of $\mathrm{Cr}^{2+}, \mathrm{Mn}^{2+}$, $\mathrm{Fe}^{2+}$ and $\mathrm{Co}^{2+}$ are $d^4, d^5, d^6$ and $d^7$ respectively. Which one of the following will exhibit minimum paramagnetic behaviour?
(At. no. $\mathrm{Cr}=24, \mathrm{Mn}=25, \mathrm{Fe}=26, \mathrm{Co}=27$ )

Options:
A $\left[\mathrm{Fe}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+}$
B $\left[\mathrm{Co}\left(\mathrm{H}_2 \mathrm{O}_6\right]^{2+}\right.$
C $\left[\mathrm{Cr}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+}$
D $\left[\mathrm{Mn}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+}$

The correct answer is:
$\left[\mathrm{Co}\left(\mathrm{H}_2 \mathrm{O}_6\right]^{2+}\right.$

Solution:
No Solution Available

Topic: Chemistry, Coordination Compounds, NEET, NEET 2011 (Screening)
The deletion in chromosome number 16 results in

Options:
A pleiotropy.
B quantitative problem of RBC's.
C qualitative problem of RBC's.
D hypertrichosis.

The correct answer is:
quantitative problem of RBC's.

Solution:
When there is deletion or mutation in the chromosome number 16 results in Thalassemia wherein there is very low or nil production of the alpha globins for making haemoglobin making it a quantitative problem as compared to a sickle cell which is quantitative issues of making faulty Hb.

Topic: Biology, Principles of Inheritance and Variation, NEET
The density of $1 \mathrm{M}$ solution of a compound ' $X$ ' is $1.25 \mathrm{~g} \mathrm{~mL}^{-1}$. The correct option for the molality of solution is (Molar mass of compound $X=85 \mathrm{~g}$ )

Options:
A $1.165 \mathrm{~m}$
B $0.858 \mathrm{~m}$
C $0.705 \mathrm{~m}$
D $1.208 \mathrm{~m}$

The correct answer is:
$0.858 \mathrm{~m}$

Solution:
Relation between Molality ( $m$ ), Molarity (M) and density (d) is
$m=\frac{1000 M}{1000 \times d-M \times M_{\text {solute }}}$
Msolute denotes molar mass of solute.
$m=\frac{1000 \times 1}{(1000 \times 1.25)-(1 \times 85)}=\frac{1000}{1250-85}=\frac{1000}{1165}$
$\mathrm{m}=0.858 \mathrm{~m}$

Topic: Chemistry, Some Basic Concepts of Chemistry, NEET, NEET 2023 (Manipur)
The density of $2 \mathrm{M}$ aqueous solution of $\mathrm{NaOH}$ is $1.28 \mathrm{~g} / \mathrm{cm}^3$. The molality of the solution is [Given that molecular mass of $\left.\mathrm{NaOH}=40 \mathrm{~g} \mathrm{~mol}^{-1}\right]$

Options:
A $1.20 \mathrm{~m}$
B $1.56 \mathrm{~m}$
C $1.67 \mathrm{~m}$
D $1.32 \mathrm{~m}$

The correct answer is:
$1.67 \mathrm{~m}$

Solution:
Given, molarity $=2 \mathrm{M}$ [i.e 2 mole $\mathrm{NaOH}$ in $1 \mathrm{~L}$ solution]
Density $(\mathrm{d})=1.28 \mathrm{~cm}^{-3}$
Molecular weight of $\mathrm{NaOH}=40 \mathrm{gmol}^{-1}$
We know that,
$$
\begin{aligned}
& \text { Density }=\frac{\text { mass of solution }}{\text { volume of solution }} \\
& \therefore \text { Mass of solution }=1.28 \mathrm{~g} \mathrm{~cm}^{-3} \times 1000 \mathrm{~mL}=1280 \mathrm{~g} \\
& \text { Moreover, molarity } \\
& =\frac{\text { number of moles of solute }}{\text { volume of solution }(\text { in } \mathrm{mL})} \times 1000 \\
& \therefore \quad 2=\frac{\text { mass of solute }}{40 \times 1000} \times 1000=80 \mathrm{~g} \\
& \text { Now, mass of solution }=\text { mass of solvent }+ \text { mass of } \\
& \text { solute } \\
& 1280 \mathrm{~g}=\text { mass of solvent }+80 \\
& \therefore \text { Mass of solvent }=1280-80=1200 \mathrm{~g}=1.2 \mathrm{~kg} \\
& \text { Now, molality }=\frac{\text { number of moles of solute }}{\text { mass of solvent }(\text { in kg) }} \\
& =\frac{2}{1.2}=\frac{20}{12}=\frac{5}{3}=1.67 \mathrm{~m} \\
&
\end{aligned}
$$
Alternative method
Molality $(\mathrm{m})=\frac{\mathrm{M}}{1000 \mathrm{~d}-\mathrm{M} \omega \mathrm{t}} \times 1000$
where, $M=$ molarity, $d=$ density of solution
$$
\mathrm{M} \omega \mathrm{t}=\text { molar mass of solute. }
$$
On substing the given values, we get
$$
\begin{aligned}
\text { Molality } & =\frac{2}{1000 \times 1.28-40} \times 1000 \\
& =\frac{2}{1280-40} \times 1000=\frac{2000}{1240}=1.612 \mathrm{~m}
\end{aligned}
$$

Topic: Chemistry, Solutions, NEET, NEET 2019 (Odisha)
The density of 3 M solution of Na2S2O3 is 1.25 g/mL . What is % by weight of Na2S2O3 ?

Options:
A 36.24
B 37.92
C 40.24
D 38.34

The correct answer is:
37.92

Solution:
% by weight of Na 2 S 2 O 3  =  wt. of  Na 2 S 2 O 3 wt. of solution  × 100
=4741250Ã100=37.92

Topic: Chemistry, Some Basic Concepts of Chemistry, NEET
The density of 3 M solution of NaCl is 1.25 g mL–1. What is the molality of this solution?

Options:
A 2.79m
B 3.08m
C 2.54m
D 3.16m

The correct answer is:
2.79m

Solution:
Correct Option is : (A)
2.79m

Topic: Chemistry, Some Basic Concepts of Chemistry, NEET
The density of a gas at normal pressure and 27 oC temperature is 24 units. Keeping the pressure constant, the density at 127 oC in same units will be

Options:
A 6
B 12
C 18
D 24

The correct answer is:
18

Solution:
Pressure is P=ÏRTM
Hence at constant pressure, ÏT= constant
âÏ1Ï2=T1T2
â24Ï2=273+127273+27=400300
âp2=18 units

Topic: Physics, Thermodynamics, NEET
The density of a gas is 1.964  g dm −3 at 273 K and 76 cm Hg. The gas is

Options:
A CH4
B C2H6
C CO2
D Xe

The correct answer is:
CO2

Solution:
pV=nRT
or pV=wMRT
or M=wVRTp
or M=dRTp
d=1.964 g/dm3=1.964Ã10-3 g/cc
p=76 cm Hg=1 atm
R=0.0812 L atm K-1 mol-1
=82.1 cc atm K-1 mol-1
T=273 K
M=1.964Ã10-3Ã82.1Ã2731=44
The molecular weight of CO2 is 44.
So, the gas is CO2.

Topic: Chemistry, States of Matter, NEET
The density of a liquid in the CGS system is 0.625 0.625 g cm-3. What is its magnitude in SI system?

Options:
A 0.625
B 0.0625
C 0.00625
D 625

The correct answer is:
625

Solution:
N 1 U 1 = N 2 U 2 N 1 [ M 1 L 1 â3 ]= N 2 [ M 2 L 2 â3 ]
â´ N 2 = N 1 [ M 1 M 2 ]Ã [ L 1 L 2 ] â3 =0.625[ 1g 1kg ]Ã [ 1cm 1m ] â3 =0.625Ã 10 â3 Ã 10 6 =625

Topic: Physics, Units and Dimensions, NEET