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 ?

What is the limitation of the reaction given in question 2?

Write chemical equations for the following word equations and balance them.

(a) Carbon + Oxygen ⟶ Carbon dioxide

(b) Nitrogen + Oxygen ⟶ Nitrogen monoxide

(c) Calcium + Nitrogen ⟶ Calcium nitride

(d) Calcium oxide + Carbon dioxide ⟶ Calcium carbonate

(e) Magnesium + Sulphuric acid ⟶ Magnesium sulphate + Hydrogen

(f) Sodium reacts with water to form sodium hydroxide and hydrogen.