If the capacitance of a nanocapacitor is measured in terms of a unit $'u'$ made by combining the electronic charge $'e'$, Bohr radius $'a_0$, Planck's constant $'h'$ and speed of light $'c'$ then :

Question

( A ) $u = \frac{e^2 a_0}{hc}$
( B ) $u = \frac{hc}{e^2 a_0}$
( C ) $u = \frac{e^2 c}{ha_0}$
( D ) $u = \frac{e^2 h}{c a_0}$