Introduction:
Baking soda is a common household ingredient that is widely used in baking and cooking. It is known for its ability to react with acidic ingredients, producing carbon dioxide gas, which helps dough or batter to rise. Baking soda has the chemical formula NaHCO3 and is also known as sodium bicarbonate.

Explanation:
Baking soda is primarily composed of sodium bicarbonate, which is why option A, sodium bicarbonate, is the correct answer. Let's understand why the other options are not correct:

a) Sodium bicarbonate:
Also known as baking soda, sodium bicarbonate is a white crystalline compound that is slightly alkaline. It is commonly used as a leavening agent in baking and cooking.

b) Sodium carbonate:
Sodium carbonate, also known as soda ash or washing soda, is a different compound from baking soda. It has the chemical formula Na2CO3 and is used in various industrial applications such as glass manufacturing and water treatment.

c) Calcium hydrogen carbonate:
Calcium hydrogen carbonate is not the compound known as baking soda. It is a different chemical compound with the formula Ca(HCO3)2. It is commonly found in mineral springs and is involved in the formation of stalactites and stalagmites in caves.

d) Calcium carbonate:
Calcium carbonate is another compound that is not synonymous with baking soda. It has the chemical formula CaCO3 and is commonly found in natural sources such as limestone, marble, and shells. Calcium carbonate is used in various applications, including as a dietary supplement and antacid.

Conclusion:
In conclusion, baking soda is the common name for sodium bicarbonate (NaHCO3). It is widely used in baking and cooking as a leavening agent. The other compounds mentioned in the options (sodium carbonate, calcium hydrogen carbonate, and calcium carbonate) are different chemical compounds and not interchangeable with baking soda.

A. Sodium hydrogen carbonate