A pattern using X and O is given with one term missing. Choose the correct term that will complete the sequence: XX, XOX, XXXX, XXOXX, XXXXXX, ?

Introduction / Context:
Instead of alphabet letters, this question uses a pattern made of the symbols X and O. The series is XX, XOX, XXXX, XXOXX, XXXXXX, ?. You must identify how the string length and the placement of O change from term to term, and then determine which option represents the correct next pattern.

Given Data / Assumptions:

• Series: XX, XOX, XXXX, XXOXX, XXXXXX, ?
• Each term consists of X and possibly O.
• The number of symbols and the presence of O follow a regular pattern.
• Options give candidate strings for the missing term.

Concept / Approach:
We analyse two aspects: the total length of each term and the number and placement of the O symbol. Many pattern questions like this grow in length by one each step, and alternate between having no O and having a single O in the centre. By tracking both growth and structure, we can determine the correct next term.

Step-by-Step Solution:
Step 1: Count the length and Os in each term. Term 1: XX → length 2, Os = 0. Term 2: XOX → length 3, Os = 1 (center). Term 3: XXXX → length 4, Os = 0. Term 4: XXOXX → length 5, Os = 1 (center). Term 5: XXXXXX → length 6, Os = 0. Step 2: Observe the length pattern: 2, 3, 4, 5, 6. So the next length should be 7. Step 3: Observe the presence of O: 0, 1, 0, 1, 0. This alternates between no O and one central O. Step 4: Following the alternation, after a term with 0 Os (XXXXXX), the next term should contain exactly one O, and it should be in the centre of a length-7 string. Step 5: A length-7 string of Xs with one central O should look like XXXOXXX (three Xs, then O, then three Xs).

Verification / Alternative check:
Check the candidate term XXXOXXX: length 7, one O in the centre. This perfectly continues the pattern of increasing lengths from 2 to 7 and the alternation of 0 Os, 1 O, 0 Os, 1 O, 0 Os, 1 O. Therefore XXXOXXX is a strong and unique fit.

Why Other Options Are Wrong:
Option A (XXXOXXXX): Length is 8, not 7, and it contains one O but not in a strict symmetric centre. Option C (XXXXXXX): Length 7 but has 0 Os, which breaks the alternation pattern. Option D (XXXOXXXO): Length 8 and contains two Os, violating both the length and the single-O rule.

Common Pitfalls:
Candidates may focus only on length and ignore the pattern of O, or notice only the presence or absence of O without checking exact position. Some also assume that length remains constant, which it does not. Always check both the total number of symbols and the internal symmetry or placement of special symbols in pattern questions.

Final Answer:
The string that correctly completes the series is XXXOXXX, which is option B.