Select the letter-cluster from among the given options that can replace the question mark (?) in the following series. DAG, FCI, ?, JGM, LIO

Correct — D.
Rule: +2 at every position, read down the series.

First letters: D, F, _, J, L → the gap is H.
Second letters: A, C, _, G, I → E.
Third letters: G, I, _, M, O → K.

The missing term is HEK → option (d).

Why the others are wrong

• (a)
  WUG — WUG starts with W, but the first letters climb D, F, _, J, L in twos, so the gap between F and J must be H.
• (b)
  YOI — YOI fails at the first letter too: between F and J comes H, not Y. Its last letter I also repeats FCI's instead of moving on to K.
• (c)
  HOK — HOK gets H and K right but not the middle. The second letters run A, C, _, G, I, so the gap is E, not O.

A letter-cluster series is three number series laid side by side. Convert letters to positions (A = 1 … Z = 26) and read one position at a time down the terms.

Here the first letters are D(4), F(6), H(8), J(10), L(12), and the other two columns step by 2 as well. A missing middle term must fit both neighbours: FCI + 2 gives HEK, and HEK + 2 gives JGM.

Key facts

• A = 1 through Z = 26 is the position code these series run on.
• D, F, H, J, L are positions 4, 6, 8, 10, 12: a step of 2.
• A missing middle term equals the term before plus the step, and the term after minus the step.

Common traps

• Checking only the first and last letters, where HOK and HEK agree
• Filling the gap from the left neighbour alone without checking it against JGM

No directly related past PYQ was found.