A negetively charged oil drop of mass $ 8 \times 10^{-15} \;kg$ remains suspended in a uniform field of $ 2\times 10^4 \;v/m$ in millikani experiment . The number of electrons making up the charge is $(g= 10\;m/s^2)$

Question

$\begin{array}{1 1} 20 \\ 25 \\ 40 \\ 45 \end{array} $