Select the set in which the numbers are related in the same way as are the numbers of the given set. (NOTE : Operations should be performed on the whole numbers, without breaking down the numbers into its constituent digits. E.g. 13 – Operations on 13 such as adding /subtracting/multiplying etc. to 13 can be performed. Breaking down 13 into 1 and 3 and then performing mathematical operations on 1 and 3 is not allowed.)
(4, 81, 5)
(3, 144, 9)

Correct option is A

In this question following logic is followed-
(1^st + 3^rd )² = 2^nd Number
4, 81, 5 → (4 + 5)² = 9² = 81
3, 144, 9 → (3 +9)² = 12² = 144
Similarly,
2, 100, 8 → (2 + 8)² = 10² = 100
Therefore, the correct answer is (a).