From the given choices select the odd one out.

In a letter-series item, each set of letters usually advances from one letter to the next by the SAME fixed number of alphabet positions (using A = 1, B = 2, ... Z = 26). The odd set out is the one whose gap between consecutive letters is NOT constant.

1. ADG: A(1) to D(4) is a gap of 3, and D(4) to G(7) is a gap of 3 - a constant gap of 3.

2. HKN: H(8) to K(11) is a gap of 3, and K(11) to N(14) is a gap of 3 - a constant gap of 3.

3. MPS: M(13) to P(16) is a gap of 3, and P(16) to S(19) is a gap of 3 - a constant gap of 3.

4. PSW: P(16) to S(19) is a gap of 3, but S(19) to W(23) is a gap of 4 - the gap changes partway through.

ADG, HKN, and MPS all share the identical +3, +3 pattern, while PSW alone shifts to +3, +4, so PSW does not fit the shared rule. Hence PSW is the odd one out.