Final answer:
In calcium nitride, the cation is calcium (Ca) with a charge of +2. This is because calcium loses two valence electrons to become stable and isoelectronic with argon.
Step-by-step explanation:
For calcium nitride, the charge of the cation, which is calcium (Ca), is +2 Then calcium loses its two valence electrons, it attains a stable electronic configuration, becoming isoelectronic with the noble gas argon (Ar). The resulting calcium cation is represented as Ca²⁺. In an ionic compound, the total charge must be neutral. For instance, in calcium nitride (Ca3N2), there are two nitride anions with a 3- charge, thereby requiring three Ca²⁺ cations to balance the charge. Similarly, for compounds with polyatomic ions like nitrate (NO3⁻), parentheses are used around the polyatomic ion when more than one unit is needed, as seen in calcium nitrate, Ca(NO3)2.