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.

PRQ FHG WYX KLM

KLM

Option 1:  PQR ⇒ PRQ Option 2:  FGH ⇒ FHG Option 3:  WXY⇒ WYX Option 4:  KLM ⇒ KMN Therefore, option (4) is correct option.