For each of the following pairs of ions, write the formula of the compound they will form:
(a) K⁺, O₂⁻
(b) NH₄⁺, PO₄₃⁻
(c) Al₃⁺, O₂⁻
(d) Na⁺, CO₃₂⁻
(e) Ba₂⁺, PO₄₃⁻