A particle having a charge of $\;2 \mu C\;$ is placed directly below and at a separation of 10 cm from the bob of a simple pendulum at rest . What charge should the bob be given so that the string becomes loose ? mass of the bob is 1 kg .

Question

$(a)\;5.5\times10^{-6} C\qquad(b)\;55\times10^{-6} C\qquad(c)\;0.55\times10^{-6} C\qquad(d)\;5.5\times10^{-8} C$