Answer:

A. Butter Cake

if you are adding flour to butter and sugar, you should immediately stop mixing once you no longer see any white powder.You may have read that when you overmix cake batter, the gluten in the flour can form elastic gluten strands resulting in a more dense, chewy texture. This can be beneficial in cookies, but it’s not so great in cakes and it’s an archenemy of flaky pie crusts. I’d heard that as well, but until I saw a great visual of an over-mixed cake, I’d never thought to purposely make an over-mixed cupcake to see (and taste) what happens.

B. Sponge Cake

For sponge cakes, there is only a minimal amount of liquid and the flour is gently folded in so the cake should be tender. However, over-mixing will tend to knock out the air that has been beaten into the butter, sugar and eggs so over-mixing is more likely to lead to a cake which doesn't rise properly. For pastry the fat is rubbed into the flour first and the fat coats the glutens, protecting them to an extent from the liquid when it is added. But again, too much liquid or rough handling will start to develop the gluten and result in a tough pastry.

I hope it help:)