Classification (letter triads – step pattern): In three triads, the jumps are +2 then −4 in alphabet positions; one triad breaks this pattern. Identify the odd triad.

Introduction / Context:
Letter-series classification often relies on fixed incremental jumps between characters using alphabet indices (A=1 … Z=26). Here, most triads follow +2 then −4. The outlier deviates in the second jump. We must compute differences and select the deviation.

Given Data / Assumptions:

• Triads: LNJ, RTP, NPK, FHD.
• Alphabet positions: A=1 … Z=26.
• Pattern to test: +2 then −4 between successive letters.

Concept / Approach:
Translate each triad to numbers and compute deltas (second − first, third − second). The odd one will not match (+2, −4).

Step-by-Step Solution:

Verification / Alternative check:
Reverse-check by reconstructing: Start with N; +2 gives P; applying −4 should give L, not K. Hence mismatch is confirmed.

Why Other Options Are Wrong:

Common Pitfalls:
Off-by-one errors when mapping letters to positions. Always count inclusively from the starting letter to avoid slips.

Final Answer:
NPK