Which of the following is not correct?

If we drop a 10Ib iron ball and 1Ib aluminium ball from the top of a high platform inside a mine, then both will reach the floor at the same time.

The gravitational force of attraction between the two bodies increases when their masses are increased and distance is reduced.

We do not observe small objects moving towards each other because frictional force balances the gravitational pull.

When a body is thrown up, the acceleration due to gravity at the topmost point is zero because velocity of the body is zero.