Baking powder is a fine white powder which is a leavening agent which is a combination of an acid (cream of tartar) and alkaline (baking soda). It is responsible for rise in doughs, batters etc. Thus recipes which contain an acid like lemon juice, curds, buttermilk etc will activate baking powder more effectively. Do note that excess baking powder will cause the product to collapse while less baking powder will make it heavy.
100g Baking powder