Question

what is baking powder?how does it make the cake soft and spongy?

Answer 1

Baking powder is a dry chemical leavening agent, a mixture of a carbonate or bicarbonate and a weak acid, and is used for increasing the volume and lightening the texture of baked goods.

Answer 2

Baking powder is a mixture of baking soda and an edible acid such as tartaric acid or citric acid.

When baking powder is added to water it reacts with acid (like tartaric acid or citric acid) to form carbon dioxide. This carbon dioxide trapped in the wet dough and bubbles out slowly making cake soft and spongy.