Answer :
Given that,
Time period of simple pendulum is 1.55 s.
Time period of simple pendulum for A student =1.25 s
Time period of simple pendulum for B student =1.5 s
We know that
The accuracy is defined as how close a measurement is to a known value .
The result of student of A is 1.25 s. It is more precise because it has more significant figure than student B's result of 1.6 s.
But the measurement made by student B's is much closer the known value of 1.55 s.
Hence, The most probable source of error is the result of student A.