Four letter-clusters have been given, out of which

Solution

The logic followed here is that second letter of the word is the 4 th preceding letter of the first letter and the third letter is the 6 th preceding letter of the second letter of the given word and the fourth letter is the 4 th preceding letter of the third letter. In [NJDZ] → N - 4 = J; J - 6 = D; D - 4 = Z In [BXRN] → B - 4 = X; X - 6 = R; R - 4 = N In [XTNJ] → X - 4 = T; T - 6 = N; N - 4 = J In [WSOK] → W - 4 = S; S - 6 = M; M - 4 = I So, 'WSOK' is the letter-cluster that is different.