Capacitance $C = \frac{Charge}{potential} = \frac{q}{V}$ Also potential $= \frac{work}{charge}$ $\left( \because V = \frac{W}{q} \right)$ $\therefore\ \ \ C = \frac{q^{2}}{J}$ as well as $C = \frac{J}{V^{2}}$. Thus, (a), (c), (d) are equivalent to farad but (b) is not equivalent to farad.