Four letter-cluster have been given out of which three are alike in some manner, while one is different. Choose the odd one.

ENR

1   2    3    4   5    6   7     8    9  10  11  12  13

 A   B   C    D   E    F   G    H    I    J    K    L   M

 ↓    ↓    ↓    ↓    ↓     ↓   ↓    ↓     ↓   ↓    ↓    ↓    ↓

 Z   Y    X   W   V    U   T    S    R   Q   P    O   N

26  25  24  23  22  21  20  19  18  17  16  15  14

THE LOGIC;

1) MLY,

M(13) L(12) Y(25)

= 25-13 = 12

2) DGK,

D(4) G(7) K(11)

= 11-4 = 7

3) QFW,

Q(17) F(6) W(23)

= 23-17 = 6

4) ENR,

E(5) N(14) R(18)

= 18-5 = 13

Thus, ENR is the odd one.