In the following alphabet series U, T, R, O, K, which letter should replace the question mark to correctly continue the pattern?

Introduction / Context:
This question tests your understanding of alphabet series and the ability to recognise a pattern in decreasing letter positions. Such questions are very common in aptitude and competitive exams and usually require you to map letters to their numerical positions in the English alphabet. Once that mapping is clear, the apparently random letters form a simple numeric sequence. Developing fluency with these patterns helps you solve many questions quickly in reasoning sections.

Given Data / Assumptions:
- The given series is: U, T, R, O, K, ? - Only English capital letters are used. - The pattern is assumed to be consistent throughout the sequence. - Each letter can be mapped to its position: A = 1, B = 2, ..., Z = 26.

Concept / Approach:
The basic approach is to convert each letter of the series into its numeric position in the alphabet. After conversion, we observe the differences between consecutive terms and try to identify a regular pattern. Many alphabet series follow arithmetic progressions, alternating step sizes, or increasing and decreasing step differences. Once the pattern in numbers is clear, we convert the resulting position back into a letter to obtain the missing term. Throughout this process, we treat the alphabet as an ordered list from 1 to 26 without wrapping around, since the letters here remain well within that range.

Step-by-Step Solution:
Step 1: Convert each letter to its numeric position. U = 21, T = 20, R = 18, O = 15, K = 11. Step 2: Find the differences between consecutive terms. From U (21) to T (20): difference = -1. From T (20) to R (18): difference = -2. From R (18) to O (15): difference = -3. From O (15) to K (11): difference = -4. Step 3: Observe the pattern in the differences: -1, -2, -3, -4. Step 4: The next logical difference is -5. Step 5: Apply -5 to the last known term K. K is 11, so 11 - 5 = 6. Step 6: Convert 6 back to a letter: 6 corresponds to F.

Verification / Alternative check:
To verify, rewrite the series with positions: 21, 20, 18, 15, 11, 6. Now check the successive differences again: 21 - 20 = 1, 20 - 18 = 2, 18 - 15 = 3, 15 - 11 = 4, 11 - 6 = 5. The absolute values form a simple increasing sequence 1, 2, 3, 4, 5. This confirms that the chosen missing term F (position 6) is fully consistent with the established pattern of decreasing values with increasing step size. No other option will maintain this exact numeric difference pattern.

Why Other Options Are Wrong:
A) G has position 7, which would give 11 - 7 = 4, breaking the required difference of 5. B) H has position 8, which would lead to an incorrect difference and destroy the simple 1, 2, 3, 4, 5 pattern. C) E has position 5, which produces a difference of 6 instead of 5 and does not fit the progression. Therefore, only F keeps the series consistent.

Common Pitfalls:
Many learners try to guess the answer visually without converting letters to numbers, which often leads to confusion. Another common mistake is to assume a constant difference and ignore the possibility of an increasing or decreasing step size. Some students also forget to check all the gaps in the series and focus only on the last two letters. For exam accuracy, always verify the pattern across the entire series instead of relying on intuition. Writing down letter positions and differences systematically greatly reduces errors in such questions.

Final Answer:
The letter that correctly completes the alphabet series U, T, R, O, K, ? is F.