Four letter-clusters have been given, out of which three are alike in some manner and one is different. Select the one that is different. Note: The odd one out is not based on the number of consonants/vowels or their position in the letter cluster.

Correct — C.
Rule: inside each cluster the letters step +3, +3.

KNQ: K(11), N(14), Q(17)
SVY: S(19), V(22), Y(25)
BEH: B(2), E(5), H(8)

Those three all run +3 then +3.

ILN: I(9), L(12), N(14) — that is +3 then +2. The second gap breaks the pattern, so option (c) is the odd one out.

Why the others are wrong

• (a)
  KNQ — KNQ runs K(11), N(14), Q(17), so both gaps are +3 and it sits with the majority.
• (b)
  SVY — SVY runs S(19), V(22), Y(25) — again +3 and +3, the same shape as the rest.
• (d)
  BEH — BEH runs B(2), E(5), H(8), both gaps +3, so it is not the outlier.

Letter-cluster items are arithmetic in disguise. Replace each letter by its position (A=1 up to Z=26), write the gaps, and the odd one usually announces itself.

The stem's note is doing real work: by ruling out vowel and consonant counts it tells you the difference must be positional, so you do not waste time on letter types.

Three clusters agreeing on a gap and one disagreeing is the standard construction — you are looking for the single cluster whose gap sequence differs, not for anything about meaning.

Key facts

• A=1, B=2 and so on to Z=26 is the numbering the whole family rests on.
• KNQ, SVY and BEH each step +3 then +3.
• ILN steps +3 then +2, which is what makes it different.
• The stem's note rules out vowel and consonant counts, so the rule has to be positional.

Common traps

• Counting vowels, which the stem's note explicitly rules out
• Mis-numbering the back half of the alphabet, where L=12 and N=14 are easy to slip

No directly related past PYQ was found.