What is the $S.I$unit of potential difference
A) $ohm$
B) $Volt$
C) $Coulomb$
D) $Ampere$

Hint:Here we describe the definition of potential difference and then if we are given the current and the resistance, the general formula will calculate the unit of potential difference. By dividing the potential energy by the quantity of charge, the electric potential is obtained.
Useful formula:
The formula of potential difference is given below,
$V = I \times R$
Where,
 $V$ Potential difference
 $I$ Current
 $R$ Resistance

Complete step by step solution:
Potential difference between two points is the work done in moving a unit positive charge between the two points. That represents the work involved or energy released in transfer of a unit quantity of electricity from one point to the other.
The potential difference
\[1{\text{ }}volt{\text{ }} = One{\text{ }}volt\] is the potential difference between two points in a current carrying conductor when \[1{\text{ }}joule\]of work is done to move a charge of \[1{\text{ }}coulomb\] from one point to the other. \[1\;Volt = 1\;Coulomb1\;Joule\]​
It is the difference of potential that would carry one ampere of current against one \[ohm\] resistance.
The formula of potential difference
We know that,
$V = I \times R$
The potential difference is measured by an instrument called voltmeter.
The $S.I$ unit of potential difference is \[volt{\text{ }}\left( V \right).\] The $S.I$ unit of current is $Ampere$. The $S.I$ unit of resistance is $ohm$
Hence, option B is the correct answer.
The $S.I$ unit of potential difference is \[volt{\text{ }}\left( V \right).\]

Note:When we need to calculate the possible difference between any two wire ends. We can either connect a potentiometer that gives the value of the potential difference between the ends in terms of length or, using the ammeter and the wire resistance, we can calculate the current flowing through the wire.