Friction is a ………….. force.

A non-conservative force is defined as a force whose work done depends on the path taken to move from one point to another.

Friction is a type of force for which if we calculate the work done, then it depends on the path taken in the virtue of force. For different path work done can be different. Friction is not associated with potential only because it is a non-conservative force.

Friction is a non-conservative force because work done by friction force depends on the path taken from point one to another.

Hence, the correct answer is option $4$.