Three of the following four letter-clusters are alike in a certain way and one is different. Pick the odd one out.

Correct option is D

Now, let's compare the differences in all the clusters:
Option (a) XLQ: X(24) –12 = L(12) + 5 = Q(17) Differences are 12 and 5
Option (b) ZNS: Z(26) – 12 = N(14) + 5 = S(19) Differences are 12 and 5
Option (c) QEJ: Q(17) – 12 = E(5) + 5 = J(10) Differences are 12 and 5
Option (a) WKO: W(23) – 12 = K(11) + 4 = O(15) Differences are 12 and 4
The first three clusters (XLQ, ZNS, QEJ) have differences of 12 and 5, while WKO has differences of 12 and 4.
Therefore, the odd one out is (d) WKO.