A letter series is given with one term missing. Choose the correct alternative that will complete the series: DE, BG, YJ, ?

Introduction / Context:
This is another alphabet series question where each term contains two letters. To solve such problems, you need to analyse both the first letter sequence and the second letter sequence separately. The series DE, BG, YJ, ? follows a non simple pattern that involves forward and backward movement through the alphabet, so careful observation is required.

Given Data / Assumptions:

• Series: DE, BG, YJ, ?• Each term has two letters.• The first letters form the sequence D, B, Y, ?• The second letters form the sequence E, G, J, ?

Concept / Approach:
A systematic way to tackle such problems is to convert letters into their positions in the English alphabet and then examine the pattern of differences. Often, there is one rule for the first letters and another rule for the second letters. Here, the first letters are moving backwards around the alphabet in increasing steps, while the second letters are moving forwards with increasing steps. Recognising these patterns leads us to the correct missing pair.

Step-by-Step Solution:
Step 1: Convert the first letters to numbers. D is 4, B is 2, Y is 25.Step 2: Look at the movement: from 4 to 2 the change is minus 2. From 2 to 25 we consider the alphabet in a circular way. Counting backwards, 2 minus 3 gives 25, which corresponds to a shift of minus 3.Step 3: The pattern for first letters is therefore minus 2, minus 3, and should then be minus 4. Apply minus 4 to 25. 25 minus 4 is 21, which corresponds to the letter U.Step 4: Now convert the second letters to numbers. E is 5, G is 7, J is 10.Step 5: Observe the movement: from 5 to 7 we add 2, from 7 to 10 we add 3. The pattern for second letters is plus 2, plus 3, so the next step should be plus 4.Step 6: Add 4 to 10 to get 14, which corresponds to N. Thus the missing term is UN.

Verification / Alternative check:
Check the pattern for all positions. First letters: D (4) to B (2) is minus 2, B (2) to Y (25) is minus 3 counted circularly, and Y (25) to U (21) is minus 4. Second letters: E (5) to G (7) is plus 2, G (7) to J (10) is plus 3, and J (10) to N (14) is plus 4. The consistent step increase confirms that UN fits perfectly. No other option matches both the backward increasing step pattern in the first component and the forward increasing step pattern in the second component.

Why Other Options Are Wrong:
ST has first letter S, which does not follow the minus 4 pattern from Y. RQ also fails both the calculated first and second letter positions. XY and ST only show simple consecutive letters rather than the mixed forward and backward sequence present in the given series. None of these maintain the gradual increase in step sizes, so they break the hidden arithmetic rule.

Common Pitfalls:
Students sometimes try to see only simple alphabetical sequences, such as always moving forward by the same number of letters, and overlook circular movement or changing increments. Others focus only on one position in the pair and ignore the other, leading to a partial match that is actually incorrect. The safest approach is always to convert letters to numbers, write the differences explicitly, and ensure that the same rule explains every step for both the first and second letters.

Final Answer:
The missing term that completes the series correctly is UN.