Question

when baking powder are mixed with food stuff they made food stuff sponge after cooking

Answer 1

When baking powder is heated then a decomposition reaction occurs and in the reaction carbondioxide [ CO2] is produced which enlarges the size of the eatables like cakes,buns,etc which make it very spongy and fluffy. 

Answer 2

IT IS BECAUSE BAKUNG SODA IS A leaving AGENT WHICH IS USED FOR BAKING AND COOKING TO MAKE FOOD RUSE