A the main ingredient of baking powder for baking cakes is sodium bicarbonate, which can make the baked cakes loose and porous. So, A is wrong;

B, because acid rain can react with calcium carbonate, a component of marble, acid rain has strong corrosiveness to marble building materials, so B is correct;

C. Calcium hydroxide, the main component of lime slurry, can react with carbon dioxide to generate hard calcium carbonate and attach it to the wall, thus protecting the wall. Therefore, C is correct;

D. Calcium carbonate can react with hydrochloric acid in gastric juice and can be used as calcium supplement in medical and daily health care products. Therefore, d is correct.

So choose a.