An oil drop of mass $m$, carrying $n$ extra electrons, remains at rest in the uniform electric field between two horizontal plates that are separated by distance $d$. The potential difference across the plates is $V$, the elementary charge is $e$ and the free-fall acceleration is $g$. What is the value of $n$?
- A$\frac{eV}{mgd}$
- B$\frac{mgd}{eV}$
- C$\frac{meV}{gd}$
- D$\frac{gd}{meV}$