A simple letter series is given with one term missing. Choose the correct letter that will complete the sequence: B, F, K, Q, ?

Introduction / Context:
This is a single-letter series question. You are given the sequence B, F, K, Q, ? and asked to find the next letter. These questions check how quickly you can spot numeric patterns in the positions of letters in the English alphabet.

Given Data / Assumptions:

• Series: B, F, K, Q, ?
• Each term is a single letter.
• The pattern is purely based on alphabetical positions.
• Alphabet positions: A = 1, B = 2, ..., Z = 26.

Concept / Approach:
We convert each letter to its numeric position and look for a regular pattern in the differences between consecutive terms. Many series of this type use increasing or decreasing steps, sometimes with the step size itself increasing by 1 or 2. Once the pattern is recognised, we apply it to find the next position and convert back to a letter.

Step-by-Step Solution:
Step 1: Convert each letter to its alphabet position. B = 2, F = 6, K = 11, Q = 17. Step 2: Find the differences between consecutive terms. From 2 to 6: +4. From 6 to 11: +5. From 11 to 17: +6. Step 3: The pattern in the increments is +4, +5, +6. This suggests that the next increment should be +7. Step 4: Apply the next increment to the last known term: 17 + 7 = 24. Step 5: Position 24 corresponds to the letter X.

Verification / Alternative check:
We can rewrite the series including the answer: B (2), F (6), K (11), Q (17), X (24). The increments are +4, +5, +6, +7 which forms a clear and logical pattern of increasing step sizes. There is no other letter that fits this structured growth as precisely as X does.

Why Other Options Are Wrong:
Option B (R): R is 18, and 17 to 18 would be an increment of +1, which breaks the increasing differences pattern. Option C (T): T is 20, and 17 to 20 is +3, not consistent with +4, +5, +6, +7. Option D (Y): Y is 25, so 17 to 25 is +8, skipping over the expected +7 increment.

Common Pitfalls:
A frequent error is to look for a constant increment and, when that is not found, to guess randomly. Another pitfall is to forget that the step size itself might be increasing. When the direct differences are not equal, always check if they form a pattern of their own, such as +2, +3, +4 or +4, +5, +6 and so on.

Final Answer:
The correct letter that completes the series is X, corresponding to option A.