The correct option is D CO2
Baking soda i.e. sodium hydrogen carbonate (NaHCO3) is added for faster cooking. The following reaction takes place when it is heated during cooking.
2NaHCO3(Sodium hydrogen carbonate)Heat−−→Na2CO3(Sodium carbonate)+H2O(Water)+CO2(Carbon dioxide gas)↑⏐
⏐
⏐⏐
So, gas ‘X’ is carbon dioxide, CO2.
Hence, the correct answer is option (b).