Correct option is A
Logic: 1st number × 2 = 3rd number, 2nd number × 2 = 4th number.

Lets check by options;
Option (a); IGRO (Not follow)
I × 2 = R, G × 2.148.. = O
Option (b); EMJZ (Follow)
E × 2 = J, M × 2 = Z
Option (c); CHFP (Follow)
C × 2 = F, H × 2 = P
Option (d); BLDX (Follow)
B × 2 = D, L × 2 = X
So, IGRO is odd one out.
Thus, the correct answer is (a).a