When tap water contains high levels of calcium, a substance called calcium carbonate (CaCO3) can build up at the mouths of water faucets. This buildup, called limescale, can prevent water from flowing through a faucet properly. To remove the calcium carbonate, you can scrub the faucet with citric acid (C6H8O7). Citric acid combines with calcium carbonate to form calcium citrate (Ca3C12H10O14), carbon dioxide gas (CO2), and water (H2O). The calcium citrate washes away easily, allowing water to flow through the faucet again. Which are products?

the correct answer to this question is 2

answer///carbon;

chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. these processes are called chemical reactions and, in general, are not reversible except by further chemical reactions. some reactions produce heat and are called exothermic reactions and others may require heat to enable the reaction to occur, which are called endothermic reactions. understanding chemical changes is a major part of the science of chemistry.