Simple Pendulum question from MHT CET 2023 (13 May, Shift 1)

Answer: (d)

1. Buoyancy reduces the effective weight: $g_{eff} = g\left(1 - \frac{\sigma}{\rho}\right)$.
2. $\frac{\sigma}{\rho} = \frac{1}{8} \Rightarrow g_{eff} = \frac{7g}{8}$
3. $T' = T\sqrt{\frac{g}{g_{eff}}} = \sqrt{\frac{8}{7}}\,T$
4. So the answer is (d).