* Calcium: The symbol for calcium is Ca.
* Hydrogen: The symbol for hydrogen is H.
* Phosphide: The phosphide ion is PO₃³⁻.
Since calcium has a +2 charge and the phosphide ion has a -3 charge, we need two phosphide ions and three calcium ions to balance the charges:
* 3Ca²⁺ + 2PO₃³⁻ → Ca₃(PO₃)₂
However, the name "calcium hydrogen phosphide" indicates the presence of a hydrogen atom in the formula. This means that one of the phosphate ions has a hydrogen atom attached, forming the hydrogen phosphate ion (HPO₃²⁻).
Therefore, the correct formula is CaHPO₃.
