A.Calcium and magnesium dissolve in water.
B.Calcium and magnesium evaporate on contact with the walls of the pipe.
C.Calcium and magnesium form precipitates of their respective oxides.
It's C, calcium and magnesium form precipitates of their respective oxide
The statement 'Calcium and magnesium form precipitates of their respective oxides' best describes the chemical change as it involves a reaction that transforms the calcium and magnesium into new compounds, their oxides, which can clog pipes.
The statement that best describes this change as a chemical change is C. Calcium and magnesium form precipitates of their respective oxides. This represents a chemical change because it involves a reaction that transforms the calcium and magnesium into new substances - their oxides. Here's how it works: in the presence of oxygen, calcium and magnesium in hard water can undergo an oxidation process. During this oxidation, the calcium becomes calcium oxide and the magnesium becomes magnesium oxide. These oxides are less soluble in water and form precipitates, which can accumulate and clog the pipes.
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Silicon generally forms at least polar covalent bonds, like carbon, as befits its status as a Gropu 4A nonmetal. The only obvious exception I can think of is SiC, which despite the similarity you might expect to graphite or diamond does, I think, have significant ionic or metallic character to its bonding in the solid state.
b. demonstrated how amino acids can form from the environment
c. confirmed that the ultimate source of amino acids and proteins is from plants
d. not yet determined the source of amino acids