List of top Physics Questions on coulombs law asked in BHU UET

A charged oil drop is suspended in a uniform electric field of $3 \times 10^{4}\, V / m$ so that it neither falls nor rises. The charge on the drop will be (take the mass of the drop is $9.9 \times 10^{-15} \,kg$ and $g=10 \,ms ^{-2}$ )