4T√(1/15)
T√(1/14)
2T√(1/14)
2T√(1/10)
Correct option is A. 4T√(1/15)
For simple pendulum
T=2π√(L/geff)
Situation 1: when pendulum is in air → geff = g
Situation 2: when pendulum is in liquid
geff = g(1 - ρliquid/ρbody) = g(1 - 1/16) = (15g)/16
So, T'/T = 2π√(L/(15g/16)) / 2π√(L/g) → T' = 4T√(1/15)