Find the missing group of letters in the following series: BC, FGH, LMNO, _____

The correct option is TUVWX.

Let us analyze the pattern in the given series of letter groups:
BC, FGH, LMNO, _____

First, let's look at the length (number of letters) of each consecutive group:
- First group (BC) has 2 letters.
- Second group (FGH) has 3 letters.
- Third group (LMNO) has 4 letters.
- Therefore, the missing fourth group must have 5 letters.

Next, let's analyze the transitions between the groups in the alphabet:
- The first group ends with the letter C. The next group begins with F. The skipped letters in between are D and E (2 skipped letters).
- The second group ends with the letter H. The next group begins with L. The skipped letters in between are I, J, and K (3 skipped letters).
- Following this pattern, the transition from the third group (which ends with O) to the fourth group must skip 4 letters.
- Skipping 4 letters after O (which are P, Q, R, and S) brings us to the letter T.

Since the next group starts with T and consists of 5 consecutive alphabetical letters, the letters are:
T, U, V, W, X

Thus, the missing group in the series is TUVWX.