A tiny spherical oil drop of mass 8 mg is kept suspended by applying a potential difference of 100 V between two metallic plates kept seperated by a distance 1 cm. The number of electrons on the oil drop are: (Take $g =10 ms^{-2}$)

$5 \times 10^{10}$ $5 \times 10^8$ $5 \times 10^{12}$ $5 \times 10^{13}$

$5 \times 10^{10}$

The correct answer is Option (1) → $5 \times 10^{10}$