HCI+CaCO3=CaCl2+H2O+CO2

2 HCl + CaCO3 = CaCl2 + H2O + CO2

Explanation:

On the right side we have 2xCl, to get the same amount we will multiply HCl on the left side by 2.

This will give us 2xH on the left side; we also have 2xH on the right side (in H2O).

On both sides we have 1x Ca; 1x C.

On the left side we have 3XO (in CaCO3), on the right side we have 1O in H20 and 2xO in CO2, so 3x O on the right side as well.

The reaction is balanced.