In the triplet letter series MHZ, NIW, OKT, PNQ, which of the following three letter groups should come next to continue the pattern correctly?

Introduction / Context:
This question deals with a three position letter series where each position in the triplet follows a distinct arithmetic pattern. Such series train you to manage several simultaneous progressions and are common in alphabet test sections of aptitude exams. Successfully solving them improves your skill in breaking complex patterns into simpler components and handling modular arithmetic in the alphabet.

Given Data / Assumptions:
- Given series: MHZ, NIW, OKT, PNQ, ? - Each term is a group of three letters. - A single consistent rule drives each of the three positions. - Alphabet positions are numbered from 1 to 26 for A to Z.

Concept / Approach:
The systematic way to handle such problems is to treat the first, second, and third letters as three independent numeric sequences. For each sequence, we examine how the letter position changes from term to term. The pattern may involve constant increments, varying increments, or even wrap around using modular arithmetic. After identifying each sequence rule, we extend it by one step to get the next letter for that position and then combine the three letters into the final triplet.

Step-by-Step Solution:
Step 1: Convert each term to numeric positions. MHZ: M (13), H (8), Z (26). NIW: N (14), I (9), W (23). OKT: O (15), K (11), T (20). PNQ: P (16), N (14), Q (17). Step 2: First letters sequence: M, N, O, P. Positions: 13, 14, 15, 16. This is a simple +1 increase each time. Next first letter: 16 + 1 = 17, which is Q. Step 3: Second letters sequence: H, I, K, N. Positions: 8, 9, 11, 14. Differences: +1, +2, +3. The step size is increasing by 1 each time. Next difference should be +4. 14 + 4 = 18, which corresponds to R. Step 4: Third letters sequence: Z, W, T, Q. Positions: 26, 23, 20, 17. Each step is -3. Next: 17 - 3 = 14, which is N. Step 5: Combine the results for the next term. First letter Q, second letter R, third letter N, giving QRN.

Verification / Alternative check:
Summarising, we have first letters: 13, 14, 15, 16, 17 (+1 constant). Second letters: 8, 9, 11, 14, 18 (+1, +2, +3, +4). Third letters: 26, 23, 20, 17, 14 (-3 constant). Each sequence independently obeys a neat arithmetic pattern. No other option offers a triplet where all three positions align with these numeric rules. QRN therefore satisfies all constraints simultaneously and is the unique valid continuation of the series.

Why Other Options Are Wrong:
A) QNR has N as the second letter (14) which conflicts with the required +4 jump to 18 from the previous second letter N (14). C) RNM begins with R instead of Q and does not maintain the simple +1 progression of first letters. D) QNO fails both the second and third letter patterns, so it cannot represent the correct extension.

Common Pitfalls:
A frequent mistake is to focus on only one or two positions and ignore the third, leading to partial pattern matching that does not hold overall. Another issue is forgetting that different positions can follow different types of arithmetic sequences, including increasing step sizes. To avoid these problems, always separate and fully analyse each letter position before checking options. By doing so, you will be more confident that your selected triplet fits the full multi position pattern rather than a subset of it.

Final Answer:
The three letter group that correctly completes the series MHZ, NIW, OKT, PNQ, ? is QRN.