Select the missing number in the given diagrams:

Correct option is C

Find the relation between the numbers in the first circle:

20 - 9 = 11

​$$11^2 = 121$$

Find the relation between the numbers in the second circle:

24 - 11 = 13

​$$13^2 = 169$$

Find the relation between the numbers in the third circle:

32 - 17 = 15

​$$15^2 = 225$$

Thus the correct answer is option C.