Correct option is A
Given: 10 is related to 2 and 45 is related to 9 with same logic.
Logic: 1st number 5 = 2nd number
For, 10 - 2
10 5 = 2
For, 45 - 9
45 5 = 9
Similarly,
50 - ?
50 5 = 10
So, 50 is related to 10.
Thus, correct option is (a).