Four of the following five are alike in a certain way and thus form a group. Which of the following does not belong to the group?

The pattern followed in the given letter clusters is based on opposite letters in the English alphabetical series. The 1st and 2nd letters are opposites, and the 3rd and 4th letters are opposites. Also, the 3rd letter is 2nd succeeding letter of the 1st letter. In CXEV: C and X are opposite letters. E and V are opposite letters. Also, C + 2 = E In GTIR: G and T are opposite letters. I and R are opposite letters. Also, G + 2 = I In JQLO: J and Q are opposite letters. L and O are opposite letters. Also, J + 2 = L In KPNO: K and P are opposite letters. L is the opposite of O. However, K + 2 = M ≠ N In NMPK: N and M are opposite letters. P and K are opposite letters. Also, N + 2 = P