In the following question, each option shows a group of four letters following a pattern. Select the group of letters that does not follow the same pattern as the others (odd one out).

Introduction / Context:
This question is a letter based odd one out problem, which is common in reasoning and mental ability sections of aptitude tests. The idea is to examine how letters change within each group and to find a consistent alphabet based pattern. Once the pattern is understood for most options, we can quickly see which group does not follow it and therefore must be selected as the answer.

Given Data / Assumptions:
- The options are acDD, egHH, ikLL, QSTt, and moPP.
- We assume standard alphabetical positions for letters A to Z, where A is 1, B is 2, and so on.
- Capital and small letters are considered the same in terms of alphabet position, but their case can still be part of the pattern if needed.
- Exactly one option breaks the main rule followed by the others.

Concept / Approach:
Each group has two lower case letters followed by two repeated upper case letters in most options. The first two letters appear to skip one letter in between, and the last two letters repeat a letter that comes immediately after the second letter of the group. The strategy is to check whether each group follows this pattern regarding alphabet positions and case. The group that does not match this structure is the odd one out.

Step-by-Step Solution:
Step 1: Consider acDD. Starting from a to c, one letter b is skipped, so there is a gap of 2 positions. The next letter after c is d, which appears twice as DD in upper case, so this fits the pattern.Step 2: Consider egHH. From e to g, one letter f is skipped, again a gap of 2. The next letter after g is h, which appears twice as HH, so this also fits the same pattern.Step 3: Consider ikLL. From i to k, one letter j is skipped, again a difference of 2 positions. The next letter after k is l, which appears twice as LL. This again follows the rule.Step 4: Consider moPP. From m to o, the letter n is skipped, again a gap of 2. The next letter after o is p, which appears twice as PP, so moPP also follows the same pattern.Step 5: Now examine QSTt. Here, Q and S are capital letters, not lower case, and from Q to S the gap is also 2 letters, but the repeated letter is t in a different case, not exactly matching the pattern of two identical upper case letters that immediately follow the second letter.Step 6: Therefore QSTt does not consistently match the structure of the other four options and is the odd one out.

Verification / Alternative Check:
We can verify by writing alphabet positions. For acDD, a is 1, c is 3, D is 4. For egHH, e is 5, g is 7, H is 8. For ikLL, i is 9, k is 11, L is 12. For moPP, m is 13, o is 15, P is 16. In all these, the positions follow the pattern first letter, first plus two, then repeated letter equal to second plus one. In QSTt, Q is 17, S is 19, T is 20, but the final t is lower case and breaks the consistent formation style. This confirms that QSTt is different from the others.

Why Other Options Are Wrong:
acDD is not odd because it perfectly follows the skip one, then repeat next letter pattern. egHH is also consistent with the same rule. ikLL continues the same structure and so it cannot be the odd one out. moPP also matches the pattern of using two lower case letters with a gap of two, followed by two identical upper case letters one step ahead of the second letter. Since these four fit nicely into a single rule, they are not correct choices for the odd one out.

Common Pitfalls:
Some learners may ignore letter case entirely and only look at positions, which can make QSTt appear similar at first glance. Others may focus only on the first two letters, see that all have a gap of two, and mistakenly think there is no difference. In pattern based questions, it is important to look at the full structure, including repetition, letter case, and relative positions. Careful observation prevents wrong guesses and improves accuracy in exam situations.

Final Answer:
QSTt