What happens when
$(i)$ sodium metal is dropped in water?
$(ii)$ sodium metal is heated in free supply of air?
$(iii)$ sodium peroxide dissolves in water?

(N/A) $(i)$ When $Na$ metal is dropped in water,it reacts violently to form sodium hydroxide and hydrogen gas. The chemical equation involved in the reaction is:
$2 Na_{(s)} + 2 H_2O_{(l)} \longrightarrow 2 NaOH_{(aq)} + H_{2(g)}$
$(ii)$ On being heated in air,sodium reacts vigorously with oxygen to form sodium peroxide. The chemical equation involved in the reaction is:
$2 Na_{(s)} + O_{2(g)} \longrightarrow Na_2O_{2(s)}$
$(iii)$ When sodium peroxide is dissolved in water,it is readily hydrolysed to form sodium hydroxide and hydrogen peroxide. The chemical equation involved in the reaction is:
$Na_2O_{2(s)} + 2 H_2O_{(l)} \longrightarrow 2 NaOH_{(aq)} + H_2O_{2(aq)}$