Define the unit charge.

Hint: The unit charge can be interpreted in many ways, it can be a very small charge, it can be the base charge where all other charges are derived from, or it can be the unit of charge.

Complete step by step answer:
From Coulomb’s Law, we know that the electrostatic force of attraction or repulsion between two charges is directly proportional to the product of the two charges and is inversely proportional to the square of the distance between the charges. So, it can be written as,
\[F=k\dfrac{{{q}_{1}}{{q}_{2}}}{{{r}^{2}}}\]
Where
${{\text{q}}_{\text{1}}}\text{ and }{{\text{q}}_{2}}$ are the two charges.
r is the distance between the two charges.
k is the proportionality constant whose value is $9\times {{10}^{9}}\text{ N}{{\text{m}}^{2}}{{C}^{-2}}$
If two positive unit charges are separated by a distance of 1 m, then from coulomb’s law we get the force of repulsion as $9\times {{10}^{9}}\text{ N}$.
So, we can define a unit charge as two similar charges that should be placed at a distance of 1m apart in order to get a Coulomb’s repulsive force as $9\times {{10}^{9}}\text{ N}$.
We can define the unit charge as a charge of 1 coulomb.
The unit of charge is the coulomb, and it is defined as the amount of electric charge (q) transported by a constant electric current of one ampere in one second.
Another way of defining the term ‘unit charge’ is by framing it as a fundamental charge, and all the other charges are derived from this unit charge. We can say that all other charges are fundamental multiples of the unit charge. In electrostatics, we use the charge of an electron or a proton (Both have the same magnitude of charge) as the unit charge.

Note: Coulomb can also be defined as the amount of excess charge on a capacitor of one farad charged to a potential difference of one volt.
Another way of defining the term ‘unit charge’ is by framing it as a fundamental charge, and all the other charges are derived from this unit charge. We can say that all other charges are fundamental multiples of the unit charge. In electrostatics we use the charge of an electron or a proton (Both have the same magnitude of charge) as the unit charge.