Depending on the number of oxygen atoms in the anions, the names of some acids and their formulae are given. Write the formula of their corresponding salts.

Give an example of a divalent anion and a trivalent cation. Write the formula of the compound formed by their combination.

State the number of atoms present in each of the following:

(a) PO₄^3-

(b) P₂O₅

(c) H₂SO₄

(d) SO₄^-2

What is a chemical equation ? Why it is necessary to balance it ?