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 observation giving suitable reasons.

Explanation

(a) Silver (Ag) is placed below hydrogen in the activity series. It cannot replace hydrogen from dilute HCl and no chemical reaction is possible.
(b) The reaction of aluminium (Al) with dilute HCl is of exothermic nature. Therefore, the temperature rises.
`2Al(s) + 6HCl (aq) to 2AlCl_(3)(aq) + 3H_(2)(g) + "heat"`
(c) Hydrogen gas is evolved when sodium metal (Na) is reacted with dilute HCl. The reaction is of exothermic nature. Therefore, hydrogen catches fire accompanied by explosion.
`2Na (s) + 2HCl(aq) to 2NaCl(aq) + H_(2)(g) + "heat"`
Remember : Sodium metal as such does not catch fire. It is the hydrogen gas evolved which burns since the reaction in highly exothermic in nature.
(d) Lead (Pb) reacts with dilute HCl to evolve hydrogen gas accompanied by bubbles.
`Pb(s) + 2HCl(aq) to PbCl_(2)(aq) + H_(2)(g).`