Correct choice is (b) 199 or 198
For explanation I would say: The optimum number of secondary turns in a C.T. is the value that makes the transformation ratio (R) and nominal ratio (Kn) equal. It is usually one or two turns less than the actual value. Thus in a 1000/5 A, though the number of turns would be 200 ideally, it is considered as 198 or 199 in order to keep R and Kn equal.