(i) When sodium metal is dropped in water, H₂ gas is evolved which catches fire due to the exothermicity of the reaction.

2Na (s) + 2H₂O (l) → 2NaOH (aq) + H₂ (g)

(ii) When sodium metal is heated in free supply of air, sodium peroxide (Na₂O₂) along with a small amount of sodium oxide (Na₂O) is formed.

(iii) When sodium peroxide dissolves in water, sodium hydroxide (NaOH) and hydrogen peroxide (H₂O₂) is formed.