Correct option is A
In this question following logic is followed-
(1st + 1st – 1)2 = 2nd 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).