Which gas is released when lemon juice reacts with marble stones ?

Acids with marble stones releases $C{O}_2$ gas

Gas released when lemon juice reacts with marble stones is $C{O}_2$ gas

$\text{Lemon juice}+\text{marble stone}\to {\text{CO}}_{2}gas$

White marble contains calcium carbonate $CaC{O}_3$ and lemon juice contains ascorbic acid and Citric acid. Calcium carbonate readily reacts with ascorbic acid and citric acid to from calcium ascorbate and calcium citrate and releases  $C{O}_2$ gas.