
When the bob is immersed in water its effective weight is mg′=mg−FB, where, FB is buoyant force.
Then, g′=mmg−FB =ρBVρBVg−ρWVg
=(ρBρB−ρw)g =55−1×g=54g
Now, time period of simple pendulum is given by T=2πgl
Thus, the ratio TT′=g′g=54gg=45
⇒T′=T45=2105
Thus, the new time period is T′=55s.
Hence, value of x=5.