A simple pendulum has a length $l .$ The inertial and gravitational masses of the bob are $m_{1}$ and $m_{g}$ respectively. Then the time period $T$ is given by
(a) $T=2 \pi \sqrt{\frac{m_{g} l}{m_{i} g}}$
(b) $T=2 \pi \sqrt{\frac{m_{j} l}{m_{g} g}}$
(c) $T=2 \pi \sqrt{\frac{m_{i} \times m_{g} \times l}{g}}$
(d) $T=2 \pi \sqrt{\frac{l}{m_{i} \times m_{g} \times g}}$