Which statement is not valid?
(A) Current is the speed of the charged particles that carry it.
(B) Electromotive force \[\left( {{\mathbf{e}}.{\mathbf{m}}.{\mathbf{f}}} \right)\] is the energy converted to electrical energy from other forms per unit charge.
(C) The potential difference \[\left( {{\mathbf{p}}.{\mathbf{d}}} \right)\]between two points is the work done per unit charge when moving charge from one point to the other.
(D) The resistance between the two points is the potential difference between the two points per unit charge.

Hint:We should check each option separately and we should know the definition of potential difference, emf, current.We should have an idea of work and mechanical generators.

Complete step by step answer:
Option \[A\] is, current is the speed of the charged particles that carry it. It is a wrong statement since Current is the rate of flow of electrical charge carriers like electrons per second. It is the number of electrons passing through a point in one second. Current flows from negative to positive points. The SI unit for measuring electric current is the ampere \[\left( A \right).\] one ampere of current is defined as one coulomb of electrical charge moving past a unique point in a second. Electric current is widely used in household and industrial appliances.
Option \[B,\] electromotive force \[\left( {e.m.f} \right)\]is the energy converted to electrical energy from other forms per unit charge. This is a right statement.E.m.f is the energy per unit electric charge that is imparted by an energy source, such as an electric generator or a battery. Energy is converted from one form to another in the generator or battery as the device does work on the electric charge being transferred within it.
Option \[C,\] the potential difference \[\left( {p.d} \right)\] between two points is the work done per unit charge when moving charge from one point to the other. This is a right statement. Since, the potential difference is also known as voltage, which is equal to the work done per unit charge to move the charge between two points against static electric field
Option \[D,\] the resistance between the two points is the potential difference between the two points per unit charge. This is a right statement.
So, Option (A) is the answer.

Note:Stop when you get a wrong statement.If the first option itself is wrong, then there is no need of checking other options since there is no option having two incorrect. You should be aware of basic definitions.