Question

An element x on reaction with dilute acid evolves a gas that burns with a pop sound while a compound y on reaction with dilute acid evolves a gas that turns lime water milky identify x and y

Answer 1

Here 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↑

Here the compound Y is any metal carbonate or metal bicarbonate which reacts with dil. HCl to form salt, water and CO2 gas is evolved. Let us consider here Y as sodium carbonate or sodium bicarbonate.
Na2CO3 + 2HCl → 2 NaCl + H2O + CO2↑
NaHCO3 + HCl → NaCl + H2O + CO2↑
When carbon dioxide is passed through lime water, it turns milky.
Ca(OH)2 + CO2 → CaCO3+ H2O
(milky)

Answer 2

the element x is may be k, Na,Ca,Mg,Al,Zn,fe(because these elements are more reactive then hydrogen and displaces hydrogen from its compound)
y compound is CaCO3
CaCO3+HCl=>CaCl2+CO2+H2O