The bob of a simple pendulum of period T is given a negative charge. If it is allowed to oscillate with an identical charge at the point of suspension. The new time period will be

The charge of the bob is repelled by a force F by the charge at the point of suspension. Since F is purely radial, it has no tangential component, so restoring force acting on the bob at its displaced position remains the same $\left(\mathrm{mg} \sin \mathrm{\theta }\right)$. Therefore time period remains unchanged.