Which letter cluster will replace the question mark (?) to complete the given series?
WTNM, SYHT, ? , KIVH, GNPO

The correct answer is ODBA.

To determine the missing letter cluster in the given series, we analyze the pattern followed by each letter position across the sequence:

WTNM, SYHT, ?, KIVH, GNPO

1. First letter of each cluster:
W (23) → S (19) → ? → K (11) → G (7)
Pattern: Subtract 4 from the positional value of the previous letter.

$23-4=19$

$19-4=15$

Letter 15 is O.
Verification:
$15-4=11$ (K)

$11-4=7$ (G)

2. Second letter of each cluster:
T (20) → Y (25) → ? → I (9) → N (14)
Pattern: Add 5 to the positional value of the previous letter.

$20+5=25$

$25+5=30\Rightarrow 30-26=4$

Letter 4 is D.
Verification:
$4+5=9$ (I)

$9+5=14$ (N)

3. Third letter of each cluster:
N (14) → H (8) → ? → V (22) → P (16)
Pattern: Subtract 6 from the positional value of the previous letter.

$14-6=8$

$8-6=2$

Letter 2 is B.
Verification:
$2-6=-4\Rightarrow 26-4=22$ (V)

$22-6=16$ (P)

4. Fourth letter of each cluster:
M (13) → T (20) → ? → H (8) → O (15)
Pattern: Add 7 to the positional value of the previous letter.

$13+7=20$

$20+7=27\Rightarrow 27-26=1$

Letter 1 is A.
Verification:
$1+7=8$ (H)

$8+7=15$ (O)

Combining all four obtained letters in sequence gives ODBA.