A letter series is given with one term missing. Observe the pattern in ALZ, CJV, EHR, GFN, ? and choose the correct group of letters that completes the series.

Introduction / Context:
This is a letter series question from verbal reasoning. The series ALZ, CJV, EHR, GFN, ? contains three-letter groups, and one term is missing. The task is to analyse each position within the groups (first, second, and third letters) and recognise the alphabetical pattern followed, then find the group of letters that correctly completes the series. Such problems test familiarity with alphabetical positions and pattern recognition.

Given Data / Assumptions:
Given series: ALZ, CJV, EHR, GFN, ?
Each term consists of three letters of the English alphabet.
The pattern may apply separately to the first, second, and third letters.
We assume that the same consistent rule extends to the missing term.

Concept / Approach:
The best strategy is to write down the alphabetical positions of each letter (A = 1, B = 2, ..., Z = 26) and then look at how these positions change from term to term in each of the three positions. Often the first letters follow one arithmetic sequence, the second letters follow another, and the third letters follow a third sequence, all operating independently.

Step-by-Step Solution:
First letters: A, C, E, G, ? Positions: A = 1, C = 3, E = 5, G = 7. Each time we add 2. So, next first letter: 7 + 2 = 9, which is I. Second letters: L, J, H, F, ? Positions: L = 12, J = 10, H = 8, F = 6. Each time we subtract 2. So, next second letter: 6 - 2 = 4, which is D. Third letters: Z, V, R, N, ? Positions: Z = 26, V = 22, R = 18, N = 14. Each time we subtract 4. So, next third letter: 14 - 4 = 10, which is J. Combining these, the missing group is I D J. Therefore, the correct term is IDJ.

Verification / Alternative check:
We can reconstruct the pattern: first letters increase by 2 (A, C, E, G, I), second letters decrease by 2 (L, J, H, F, D), and third letters decrease by 4 (Z, V, R, N, J). All transitions are perfectly consistent with simple arithmetic steps. IDJ is the only option that fits these three independent sequences at once.

Why Other Options Are Wrong:
Option A: JDJ has J as the first letter instead of I, breaking the +2 pattern in the first position.
Option B: IEK has E as the third letter, which does not match the required decrease of 4 to J in the last position.
Option D: JEK has incorrect letters in both the first and last positions compared with the established sequences.
Option E: HFJ does not satisfy the incremental pattern in any of the positions consistently.

Common Pitfalls:
Many candidates try to interpret the groups as whole units rather than analysing each letter position separately. Another frequent mistake is to miscalculate alphabetical positions or skip letters when counting. Writing the alphabetical index of each letter explicitly and then applying simple addition or subtraction rules usually makes such patterns much easier to see and verify.

Final Answer:
The letter group that correctly completes the series is IDJ, so the correct option is IDJ.