During the reaction of some metals with dilute hydrochloric acid,following observations were made.
$(a)$ Silver metal does not show any change.
$(b)$ The temperature of the reaction mixture rises when aluminium $(Al)$ is added.
$(c)$ The reaction of sodium metal is found to be highly explosive.
$(d)$ Some bubbles of a gas are seen when lead $(Pb)$ is reacted with the acid.
Explain these observations giving suitable reasons.

(N/A) Silver $(Ag)$ is less reactive than hydrogen in the reactivity series,so it does not displace hydrogen from dilute $HCl$.
$(b)$ The reaction between aluminium and dilute $HCl$ is exothermic,meaning it releases heat energy,which causes the temperature of the reaction mixture to rise.
$(c)$ Sodium is a highly reactive alkali metal. Its reaction with dilute $HCl$ is extremely exothermic and rapid,releasing a large amount of heat that ignites the hydrogen gas produced,making it highly explosive.
$(d)$ Lead reacts with dilute $HCl$ to form lead$(II)$ chloride and hydrogen gas. The bubbles observed are due to the evolution of hydrogen gas: $Pb(s) + 2HCl(aq) \rightarrow PbCl_2(aq) + H_2(g)$.