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

XHEP - KVRA

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;

ARNI - RMIZ

The place value of A is 01, 1st letter from reverse is Z

The place value of R is 18, 18th letter from reverse is I

The place value of N is 14, 14th letter from reverse is M

The place value of I is 09, 9th letter from reverse is R

Similarly with,

TSRA - ZIHG and OLEV - EVOL

Therefore,

XHEP - KVRA,

The place value of X is 24, 24th letter from reverse is C

The place value of H is 08, 8th letter from reverse is S

The place value of E is 05, 5th letter from reverse is V

The place value of P is 16, 16th letter from reverse is K

Thus, XHEP - KVRA is the odd one.