Assertion (A) is TRUE: electric potential is a well-defined, single-valued (state) function of position in the circuit; going around any closed loop, the charge returns to its starting potential, so the net work done is zero — consistent with Kirchhoff's voltage law (sum of emfs = sum of IR drops around a loop).

Reason (R) is TRUE and correctly explains this: potential depends only on location (not on path taken), so after completing a full loop and returning to the starting point, the potential — and hence the net work done on unit charge — is unchanged (zero net change).

Answer: Both A and R are true, and R is the correct explanation of A.