Select the option that is related to the fifth number in the same way as the second number is related to the first number and the fourth number is related to the third number.
2 : 9 : : 6 : 121 : : 5 : ?

Correct option is A

In this question following logic is followed-
(1^st + 1^st – 1)² = 2^nd Number
2 : 9 → (2 + 2 – 1)² = 3² = 9
6 : 121 → (6 + 6 – 1)² = 11² = 121
Similarly,
5 : ? → (5 + 5 – 1)² = 9² = 81
Therefore, the correct answer is (a).