Two pendulum have time period t and 5T/4 they starts SHM at the same time from the mean position the phase difference between them after the pendulum with larger period completes one oscillation is

Since, bigger pendulum completes one oscillation, it's phase is 2 pi………….(1)

The angular frequency of smaller pendulum is

w=2 pi/T. Therefore , it's phase at time 5T/4 is (according to phase equals to wt)

w 5T/4=( 2 pi/T)(5 T/4)=2.5 pi…………(2)

From (1) and (2) the difference in phase is ( pai/2).