The property of an object by virtue of which it tends to retain its state of rest or of motion is called —

1. friction
2. inertia
3. force
4. mass

inertia

Reason — If the object is in the state of rest, it will remain in the state of rest and if it is moving in some direction, it will continue to move with the same speed in the same direction unless an external force is applied on it. This property is called inertia.