What are the constituents of baking powder?

Baking soda is sodium bicarbonate, and it is alkaline in nature. Its chemical formula is ${\mathrm{NaHCO}}_3$. Baking powder is used as a leavening agent in pieces of bread and cakes. Baking powder is a mixture of baking soda (${\mathrm{NaHCO}}_3$) and mild edible tartaric acid.

Hence, ${\mathrm{NaHCO}}_3$ and tartaric acid are constituents of baking powder.