(a) How will you test for the gas which is liberated when hydrochloric acid reacts with an active metal?
​(b) Name any two active metals which can be used with hydrochloric acid to liberate the same gas.

(a) When hydrochloric acid is treated with an active metal then hydrogen gas is released.
$2\mathrm{M}+2\mathrm{HCl}\to 2\mathrm{MCl}+{\mathrm{H}}_2$
When this hydrogen gas comes in contact with burning match stick then the gas burns with a pop sound.

(b) Sodium and potassium are two active metals which can be used with hydrochloric acid to liberate the hydrogen gas.