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

The correct answer is Option 4: IMNL.

To find the odd letter-cluster, let us analyze the pattern of positional values of the letters in the English alphabet for each option:

1. RWVU:
R = 18, W = 23, V = 22, U = 21
Pattern: R (+5) → W (-1) → V (-1) → U

2. PUTS:
P = 16, U = 21, T = 20, S = 19
Pattern: P (+5) → U (-1) → T (-1) → S

3. AFED:
A = 1, F = 6, E = 5, D = 4
Pattern: A (+5) → F (-1) → E (-1) → D

4. IMNL:
I = 9, M = 13, N = 14, L = 12
Pattern: I (+4) → M (+1) → N (-2) → L

All letter-clusters except IMNL follow the pattern of adding 5 to the first letter to get the second letter, and then subtracting 1 consecutively for the next two letters (+5, -1, -1). Therefore, IMNL is the odd one out.