**Inertia: An Introduction**

Inertia is a fundamental concept in physics that describes an object's resistance to changes in its state of motion. It is the property of matter that enables an object to remain at rest or stay in motion with a constant velocity unless acted upon by an external force. The greater the inertia of an object, the more force is required to change its state of motion.

**Comparing the Rubber Ball and Stone Ball**

When comparing the rubber ball and the stone ball of the same size, we need to consider their masses. Inertia depends on the mass of an object, meaning an object with a greater mass will have more inertia.

**The Role of Mass in Inertia**

Mass is a measure of the amount of matter present in an object. It is often equated with weight, but they are not the same. Mass is a scalar quantity and is usually measured in kilograms (kg). In the case of the rubber ball and stone ball, since both have the same size, we can assume that they have the same volume and, therefore, the same mass.

**Applying the Principle of Inertia**

According to Newton's first law of motion, also known as the law of inertia, an object at rest will remain at rest unless acted upon by an external force. This means that both the rubber ball and the stone ball will remain at rest unless a force is applied to them.

**Determining the Correct Answer**

Considering that both balls have the same mass, they will have the same inertia. Therefore, the correct answer is option 'c': both balls have the same inertia.

It is important to note that the material from which the balls are made does not affect their inertia as long as their masses remain the same. Inertia is solely dependent on mass and not on the material properties of the object.

In conclusion, the statement in the question that the stone ball has more inertia than the rubber ball is incorrect. Both balls have the same inertia since they have the same mass.