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

then we check pattern 

(A) GKR

      7 11 18 

      7+11=18

the pattern is going on Fist alphabet position + second alphabet position = third alphabet position 

(B) Q I Z

     17 9 26

  17+9= 26    

the pattern is going on Fist alphabet position + second alphabet position = third alphabet position

(C) M K X

     13 11 24

     13+11 = 24

the pattern is going on Fist alphabet position + second alphabet position = third alphabet position

(D) H N U

     8 14 21

    8+14=22

then  A, B, C follow the same pattern But Option (D) is not follow the pattern 

therefore Option (D) HNU is different Ans