In the letter series BCD, RQP, LMN, TS?, which letter should replace the question mark to complete the pattern?

Introduction / Context:
This question tests your ability to recognize patterns in three letter groups of the alphabet. The given series is BCD, RQP, LMN, TS?, and you must find the missing letter in the last group. The pattern mixes ascending and descending sequences, which is common in alphabet test questions. Understanding how these short blocks are constructed is important for quickly solving similar problems in bank and SSC examinations.

Given Data / Assumptions:

• Series terms: BCD, RQP, LMN, TS?, each intended to be a three letter block.
• We use alphabet positions A 1 to Z 26.
• The first, second, and third letters inside each block may follow regular ascending or descending order.
• Exactly one option gives the correct final letter so that all blocks follow the same style of ordering.

Concept / Approach:
Within each three letter group we look at whether the letters are in ascending or descending consecutive order. BCD is clearly in ascending order, while RQP is in descending order. LMN is again ascending. This suggests that the series alternates between ascending and descending three letter sequences. The last term TS? should therefore be a descending triplet similar to RQP. That reasoning lets us decide what the third letter has to be.

Step-by-Step Solution:
Step 1: Examine the first block BCD. In alphabet positions, B 2, C 3, D 4 are consecutive in increasing order. Step 2: Examine the second block RQP. The letters R 18, Q 17, P 16 are consecutive in decreasing order. Step 3: Examine the third block LMN. The letters L 12, M 13, N 14 again form three consecutive letters in increasing order. Step 4: Observe the pattern: ascending (BCD), descending (RQP), ascending (LMN). Therefore the fourth block TS? should be a descending sequence. Step 5: For a descending block starting with T and S, we need the third letter that comes just before S in the alphabet. The letters in descending order should be T, S, R. Step 6: Thus, the question mark should be replaced by R so that the last block becomes TSR, a proper three letter descending sequence.

Verification / Alternative check:
We can now rewrite the full pattern as BCD (ascending), RQP (descending), LMN (ascending), TSR (descending). The direction of ordering alternates in a clear up down pattern: up, down, up, down. No other letter after TS will maintain this alternating structure while also giving three consecutive letters. Trying U would give TSU, which is neither strictly ascending nor strictly descending, and similarly for other options.

Why Other Options Are Wrong:
U and V both lie after T in the alphabet, so TSU or TSV break the idea of a strictly decreasing sequence. T would give TST, which repeats letters and is not consecutive. S would give TSS, where the last two letters are the same and the sequence is neither ascending nor descending. Only R gives TSR, which matches the required property of three consecutive letters in descending order.

Common Pitfalls:
A frequent error is to focus on the first block only and assume all subsequent terms must be ascending, which ignores the descending nature of RQP. Another mistake is to look at the first letters of each block and search for a pattern there, instead of noticing that the structure lies inside each group. Always check how letters behave within each chunk, especially in three letter and four letter sequences.

Final Answer:
The missing letter is R, so the last block is TSR.