Which letter group should replace the question mark in the following series,…

Concept

In an alphabet series, convert each letter to its position from A = 1 to Z = 26. Compare corresponding positions across successive groups and apply the same modular shift, wrapping after Z.

Application

1. Write the four columns separately: N, V, D, L; K, S, A, I; S, A, I, Q; and T, B, J, R.

2. In the first column, N (14) → V (22) → D (4) → L (12): each move is +8, with wraparound after Z. The next letter is T (20).

3. In the second column, K (11) → S (19) → A (1) → I (9): the same +8 rule gives Q (17).

4. In the third column, S (19) → A (1) → I (9) → Q (17): the next letter is Y (25).

5. In the fourth column, T (20) → B (2) → J (10) → R (18): the next letter is Z (26).

Cross-check

The whole group also advances by eight positions at each stage: NKST + 8 = VSAB, VSAB + 8 = DAIJ, and DAIJ + 8 = LIQR. Applying +8 once more gives TQYZ.

Result

The missing letter group is TQYZ.