Based on the English alphabetical order, three of the following four letter-clusters are alike in a certain way and thus form a group. Which is the letter-cluster that DOES NOT belong to that group? (Note: The odd man out is not based on the number of consonants/vowels or their position in the letter-cluster.)

Correct — A. Number the alphabet A = 1 to Z = 26 and write each cluster as three positions, then read the two gaps.

Rule: first letter +6 gives the second, then −3 gives the third.

FLI = 6, 12, 9 → +6, −3
MSP = 13, 19, 16 → +6, −3
AGD = 1, 7, 4 → +6, −3
CHE = 3, 8, 5 → +5, −3

Three clusters share both steps and CHE breaks the first one, so the cluster that does not belong is option (a).

Why the others are wrong

• (b)
  FLI — F(6) to L(12) is +6 and L(12) to I(9) is −3. Both steps match the group, so FLI belongs.
• (c)
  MSP — M(13) to S(19) is +6 and S(19) to P(16) is −3. It fits the pattern exactly and cannot be the misfit.
• (d)
  AGD — A(1) to G(7) is +6 and G(7) to D(4) is −3. The letters look unlike the others, but the gaps are identical, and gaps are what the question asks about.

Odd-one-out on letter clusters is a question about gaps, not about the letters. Convert to positions, take consecutive differences, and compare.

The bracketed note rules out the two shortcuts candidates reach for — vowel counting and consonant counting — which is SSC telling you the answer is positional arithmetic.

A second reading confirms it here: the distance from the first letter to the third is 3 in FLI, MSP and AGD, and only 2 in CHE.

Key facts

• A = 1 through Z = 26 is the numbering these letter-cluster items assume.
• FLI, MSP and AGD all run +6 then −3, while CHE runs +5 then −3.
• First letter to third letter is +3 in the group and +2 in CHE.

Common traps

• Comparing clusters by how the letters look instead of by position number
• Checking only one of the two gaps when the other is the one that separates the group

No directly related past PYQ was found.