Four groups of letters are given, Three of them are alike in a certain way while one is different. Choose the one which is different.

The answer is C. JF.

In each of the other three groups, the first and third letters are the same, and the second letter is the next letter in the alphabet. For example, in XT, the first and third letters are both X, and the second letter is T, which is the next letter in the alphabet after X. In RL, the first and third letters are both R, and the second letter is L, which is the next letter in the alphabet after R. In PL, the first and third letters are both P, and the second letter is L, which is the next letter in the alphabet after P.

However, in JF, the first and third letters are J and F, respectively, and the second letter is not the next letter in the alphabet after J. The next letter in the alphabet after J is K, not F.