A sodium compound X which is also used as antacid when treated witth HCl gives off an acidic gas Y. Y on passing through lime water turns it milky.
The compound X is sodium hydrogencarbonate, also known as sodium bicarbonate or baking soda. Its chemical formula is NaHCO3. Its reaction with acid is written as follows
NaHCO3 + HCl ---------> NaCl + H2O + CO2 (↑)
The compound Y is carbon dioxide, CO2. It is an acidic gas which turns lime water milky. Its reaction with lime water [Ca(OH)2] is written as
Ca(OH)2 + CO2 --------> CaCO3 + H2O