Explanation

A primary cell is not rechargeable and a secondary cell is rechargeable (usable many times), so options A and B are reversed and false. EMF is the work done per unit charge (volt = joule/coulomb); since power is work per unit time and current is charge per unit time, a volt is also a watt per ampere. Thus the emf is indeed the power provided per unit current, making option C correct. The unit of emf is the volt, not the joule, so option D is false.