The evolved gas which extinguishes a burning candle is carbon dioxide \(CO_2 \).
During chemical reaction,
Since, one of the compounds formed during this reaction is calcium chloride and as carbon dioxide is formed when dilute hydrochloric acid reacts with a metal carbonate producing effervescence , it means the metal compound is calcium carbonate \(CaCO_3 \). Hence, the compound A is calcium carbonate.
\( CaCO_3 (s) + 2HCl(aq) \)
\( ↓ \)
\( CaCl_2 (aq) + CO_2 (g) + H_2 O(l) \)