Which one of the following statements concerning emf is true?
a) emf is the work done in moving the current from one terminal to the other of an emf device.
b) emf is the work done per unit charge in moving current from one terminal to the other of an emf device.
c) emf is the force exerted on a single charge to move it from one terminal to the other of an emf device.
d) emf is the total charge moving from one terminal to the other of an emf device.
e) emf is the electromagnetic force that is exerted between the terminals of an emf device.

C) Emf is the force exerted on a single charge to move it from one terminal to the other of an emf device.

Explanation:

Electromotive force, abbreviation E or emf, electrical energy per unit supplied from an energy source, such as an electrical generator or a battery. In the engine or battery, electricity is transformed from one source to another as the device works on the electrical charge that is passed within itself.

In physics it is defined as Work done by a cell or battery in moving a unit charge from its one terminal to the other, against the potential.

Hence C is correct