Question

what flatens the large sized liquid drop

Answer 1

I hope you know about the surface tension of water. If you dont I will explain it in laymen terms. The surface of water acts as a stretched elastic layer. That is the reason a water drop is spherical in shape. But for larger drops, gravity overcomes the surface tension so the water drop becomes flat because of its weight.

hope it helps ^_^

Answer 2

gravity acting on small drops of mercury is not enough to pull down the mercury atoms from surface making it flat on earth surface. while large for large drops of mercury surface tension is not enough to keep the drops spherical because due to its weight, it flattens on surface of earth instead of being round shaped.