Question

what is the two constituents of baking powder

Answer 1

Baking powder is a mixture of baking soda and a mild edible acid like tartaric acid.

∴ Baking powder =Baking soda + mild edible acid 

Baking powder is used in preparation of cakes and breads to make it soft and pluffy.

Chemical reaction :
NaHCO3 + H⁺ions of edible acid ----> Salt of edible acid +CO2 +H2O

due to neutralization reaction of acid and NaHCO3 a salt is produced which gives sweet smell to cake.
CO2 produced will make the cake soft and pluffy.

Answer 2

Two constituents of baking powder are baking soda (sodium hydrogen carbonate) and tartaric acid

It is a mixture of baking soda (sodium hydrogen carbonate, NaHCO3) and a solid edible acid such as tartric acid.

On mixing baking powder with water which is present in the dough prepared for baking a cake or bread sodium hydrogen carbonate reacts with tartaric acid to evolve carbon dioxide gas carbon dioxide gas. This gets trapped in the wet dough and Bubbles out slowly and the cake become soft and spongy.

NaHCO3(aq) + H+(aq) ======>Na+(aq) +CO2(g)+H2O(l)

Here H+ is from tartaric acid & from sodium tartarate salt.

If however baking powder is not added in the preparation of cake or bread then the cake or bread obtained will be hard & small in size.

The advantage of using baking powder is that tartric acid present in it can react with any sodium carbonate formed and neutralize it .And the sodium tartarate salt formed by neutralisation has a pleasant taste.

hope it help