5-2 = 3, 19-16 = 3, 27-23 = 4, 31-23 = 3

In all others, 2nd number = (2 x 1 st number) + 2

Second number is the next prime number to the first number.

Second number is the reverse of the first number.

Each digit of second number is the square of the respective digit of the first number.

Second number is the difference of the square of the digits of the first number.

Except '9, 64', all number are consecutive squares.

In all the given numbers, the middle digit is twice in second group.

Only option (c) has difference if 7, rest have difference of 8 between first and second number.

9 - 2 = 7 ? 7² = 49
13 - 2 = 11 ? 11² = 121
10 - 2 = 8 ? 8² = 64 ? 61
7 - 2 = 5 ? 5² = 25