Three of the following four letter-clusters are alike in a certain way and one is different.
Select the odd one.

We know that alphabet position A=1, B=2, C=3, D=4 ......... Z=26

we check Pattern 

Option (A) GKR

                7 11 18

the pattern is  follow 7+11= 18 (first position alphabet + second position alphabet = 3rd position alphbet )

Option (B)QIZ

             17 9 26

the pattern is follow 17+9 = 26 (first position alphabet + second position alphabet = 3rd position alphbet )

Option (D) MKX

             13 11 24

the pattern is follow 13+11 = 24 (first position alphabet + second position alphabet = 3rd position alphbet )

Option (C) HNU

              8 14 21 

the pattern is follow 8+14 = 22 (first position alphabet + second position alphabet = 3rd position alphbet )

then from the above Option A, B and D is follow the same pattern But option (C) is not follow that pattern it is different 

therefore Option (C) HNU Ans