Question

a substance reacts was added to dilute hydrochloric acid to liberate a gas which burns with a Pop sound identify X and the gas evolved

Answer 1

X is a metal - Zinc
The gas liberated is Hydrogen.

Answer 2

Element X can be any metal as metals reacts with acid to form salt and produce hydrogen gas which burns with a pop sound. Let us consider X metal as Zinc here. Zinc reacts with dil. HCl to form zinc chloride and hydrogen gas.

Zn + dil 2HCl --------- ZnCl2 + H2↑