Correct Answer - Option 4 :

\(\frac{{dw}}{{dq}}\)
One Volt is equivalent to one Joule per Coulomb.

If the electrical potential difference between two points is 1 volt, then one Coulomb of charge will gain 1 joule of potential energy when moved between those two points, i.e.

\(1Volt = \frac{{1Joule}}{{1Coulomb}}\)

∴ The voltage across the element is defined as the rate of change of energy per unit charge, i.e.

\(V=\frac{{dw}}{{dQ}}\)