Correct Answer: 12

Solution : The third column is the sum of the square root of the first and the second column.

In the first column; 25 = (5)²; 36 = (6)²→5 + 6 = 11
In the second column; 49 = (7)²; 81 = (9)²→7 + 9 = 16
Similarly, In the third column; 16 = (4)²; 64 = (8)²→4 + 8 = 12

So, the missing number is 12. Hence, the first option is correct.