Which of the following has more intertia (a) a rubber ball and a stone of same size and why?

Inertia is a property of matter by which it continues in its existing state of rest or uniform motion in a straight line, unless that state is changed by an external force. It is directly proportional to the mass of the object.

In the given question, we have a rubber ball and a stone of the same size. The stone is denser and has more mass than the rubber ball of the same size. Therefore, the stone has more inertia than the rubber ball.

This is because the stone, having more mass, would require more force to change its state of motion or rest compared to the rubber ball. Hence, the stone has more inertia.