What is the proper name for CaH2?

The correct name for CaH2 is Calcium hydride. This compound consists of calcium ions (Ca²⁺) and hydride ions (H⁻). The prefix "hydride" denotes the presence of hydrogen in a binary compound with a metal.

In naming ionic compounds like this one, the metal (calcium) is named first, followed by the non-metal in its anionic form. Since calcium has a charge of +2 and each hydride ion has a charge of -1, two hydride ions are needed to balance the positive charge of one calcium ion, resulting in the formula CaH2.

The other choices represent different compounds. Calcium oxide refers to CaO, which involves calcium and oxygen. Calcium sulfate is CaSO4, containing calcium and a sulfate ion. Calcium carbonate is CaCO3, comprising calcium and a carbonate ion. Each of these compounds has distinct chemical properties and compositions differing from calcium hydride.