Given a question and a context passage, generate the answer having the word or phrase from the context passage. Here, the answer should be a shortest continous span from the passage.

Context: You are on vacation at the beach. You take your flip-flops off so you can go swimming. The sand is so hot it hurts your feet. You have to run to the water. Now imagine if it were hot enough for the sand to melt. Some places inside Earth are so hot that rock melts. Melted rock inside the Earth is called magma. Magma can be hotter than 1,000C. When magma erupts onto Earths surface, it is known as lava, as Figure 3.17 shows. Minerals form when magma and lava cool. Most water on Earth, like the water in the oceans, contains elements. The elements are mixed evenly through the water. Water plus other substances makes a solution. The particles are so small that they will not come out when you filter the water. But the elements in water can form solid mineral deposits. Fresh water contains a small amount of dissolved elements. Salt water contains a lot more dissolved elements. Water can only hold a certain amount of dissolved substances. When the water evaporates, it leaves behind a solid layer of minerals, as Figure 3.18 shows. At this time, the particles come together to form minerals. These solids sink to the bottom. The amount of mineral formed is the same as the amount dissolved in the water. Seawater is salty enough for minerals to precipitate as solids. Some lakes, such as Mono Lake in California, or Utahs Great Salt Lake, can also precipitate salts. Salt easily precipitates out of water, as does calcite, as Figure 3.19 shows. The limestone towers in the figure are made mostly of the mineral calcite. The calcite was deposited in the salty and alkaline water of Mono Lake, in California. Calcium-rich spring water enters the bottom of the lake. The water bubbles up into the alkaline lake. The Underground water can be heated by magma. The hot water moves through cracks below Earths surface. Hot water can hold more dissolved particles than cold water. The hot, salty solution has chemical reactions with the rocks around it. The water picks up more dissolved particles. As it flows through open spaces in rocks, the water deposits solid minerals. When a mineral fills cracks in rocks, the deposits are called veins. Figure 3.20 shows a white quartz vein. When the minerals are deposited in open spaces, large crystals grow. These rocks are called geodes. Figure 3.20 shows a geode that was formed when amethyst crystals grew in an open space in a rock. 
 Question: to come out of a solution as a solid
precipitate

Context: A physical change in matter is a change in one or more of matters physical properties. Glass breaking is just one example of a physical change. Some other examples are shown in Figure 3.16 and in the video below. In each example, matter may look different after the change occurs, but its still the same substance with the same chemical properties. For example, smaller pieces of wood have the ability to burn just as larger logs do. MEDIA Click image to the left or use the URL below. URL: Because the type of matter remains the same with physical changes, the changes are often easy to undo. For example, braided hair can be unbraided again. Melted chocolate can be put in a fridge to re-harden. Dissolving salt in water is also a physical change. How do you think you could undo it? Did you ever make a "volcano," like the one in Figure 3.17, using baking soda and vinegar? What happens when the two substances combine? They produce an eruption of foamy bubbles. This happens because of a chemical change. A chemical change occurs when matter changes chemically into an entirely different substance with different chemical properties. When vinegar and baking soda combine, they form carbon dioxide, a gas that causes the bubbles. Its the same gas that gives soft drinks their fizz. Not all chemical changes are as dramatic as this "volcano." Some are slower and less obvious. Figure 3.18 and the video below show other examples of chemical changes. MEDIA Click image to the left or use the URL below. URL: How can you tell whether a chemical change has occurred? Often, there are clues. Several are demonstrated in Figures 3.17 and 3.18 and in the video below. MEDIA Click image to the left or use the URL below. URL: To decide whether a chemical change has occurred, look for these signs: Gas bubbles are released. (Example: Baking soda and vinegar mix and produce bubbles.) Something changes color. (Example: Leaves turn from green to other colors.) An odor is produced. (Example: Logs burn and smell smoky.) A solid comes out of a solution. (Example: Eggs cook and a white solid comes out of the clear liquid part of the egg.) Because chemical changes produce new substances, they often cannot be undone. For example, you cant change a fried egg back to a raw egg. Some chemical changes can be reversed, but only by other chemical changes. For example, to undo the tarnish on copper pennies, you can place them in vinegar. The acid in the vinegar reacts with the tarnish. This is a chemical change that makes the pennies bright and shiny again. You can try this yourself at home to see how well it works. If you build a campfire, like the one in Figure 3.19, you start with a large stack of sticks and logs. As the fire burns, the stack slowly shrinks. By the end of the evening, all thats left is a small pile of ashes. What happened to the matter that you started with? Was it destroyed by the flames? It may seem that way, but in fact, the same amount of matter still exists. The wood changed not only to ashes but also to carbon dioxide, water vapor, and other gases. The gases floated off into the air, leaving behind just the ashes. Assume you had measured the mass of the wood before you burned it. Assume you had also trapped the gases released by the burning wood and measured their mass and the mass of the ashes. What would you find? The ashes and gases combined have the same mass as the wood you started with. This example illustrates the law of conservation of mass. The law states that matter cannot be created or destroyed. Even when matter goes through physical or chemical changes, the total mass of matter always remains the same. (In the chapter Nuclear Chemistry, you will learn about nuclear reactions, in which mass is converted into energy. But other than that, the law of conservation of mass holds 
 Question: After a physical change, matter may
look different.

Context: Iron deficiency is the most common nutritional disorder affecting at least one third of world's population. Though anemia is common manifestation of iron deficiency, other effects of iron deficiency on various tissues, organs and systems are usually under recognized. Impaired brain development and cognitive, behavioural and psychomotor impairment are most worrisome manifestations of iron deficiency. Studies have demonstrated that some of these changes occurring during period of brain growth spurt (<2 years age) may be irreversible. Association of iron deficiency with febrile seizures, pica, breath holding spells, restless leg syndrome and thrombosis is increasingly being recognized. Impaired cell-mediated immunity and bactericidal function are generally noted in iron-deficient persons; however, the findings are inconsistent. Despite proven reversible functional immunological defects in vitro studies, a clinically important relationship between states of iron deficiency and susceptibility to infections remains controversial. Studies from malaria endemic regions have reported increased incidence of malaria in association with iron supplementation. These and some other aspects of iron deficiency are reviewed in this article. 
 Question: Which deficiency is the cause of restless leg syndrome?

iron