A and B are brothers, C and D are sisters, and the son of A is the brother of D. In this family, how is B related to C?

Introduction / Context:
This blood relation question tests your ability to connect several simple family statements and identify the final relationship between two people. These problems are common in verbal reasoning sections of competitive exams and require careful tracking of parents, children, brothers and sisters without mixing them up.

Given Data / Assumptions:

• A and B are brothers, so they share at least one common parent and are of the same generation.
• C and D are sisters, so they are also of the same generation and share at least one common parent.
• The son of A is the brother of D, which places that son and D as children of the same parent or parents.
• We assume a simple family structure with no half siblings unless forced by the data.

Concept / Approach:
The key idea is to identify who the parents of C and D are. Once that is clear, we can place B correctly relative to C. If the son of A is the brother of D, then that son and D are children of A. Since C is the sister of D, C must also be a child of A. That automatically makes B, who is the brother of A, an uncle of all of A's children including C and D.

Step-by-Step Solution:
Step 1: A and B are brothers, so B is of the same generation as A.Step 2: The statement that the son of A is the brother of D means A is a parent of D.Step 3: C and D are sisters, so C must have the same parent A as D.Step 4: Therefore, C is a child of A.Step 5: B is the brother of A, so B is the paternal uncle of C.

Verification / Alternative check:
Visualise a simple tree: place A and B as siblings. Under A, place three children: C, D and the unnamed son who is D's brother. Since C is clearly a child of A and B is the sibling of that parent, B must be the uncle of C. No other consistent reading turns B into a father, grandfather or cousin of C, because that would require extra unstated connections or different generations.

Why Other Options Are Wrong:
Father is wrong because the problem clearly states that C is a child of A, not of B.Brother is wrong because B is one generation above C.Grandfather is wrong because we are only told that A and B are brothers, not that B belongs to an older generation.Cousin is wrong because cousins are children of siblings, while B himself is that sibling.

Common Pitfalls:
A frequent mistake is to think that if A's son is the brother of D, then D must belong to a different family and A is only a partial parent. However, in standard reasoning questions, brother or sister implies at least one common parent. Another error is confusing uncle with cousin when dealing with similar ages. Always fix the generations first and then decide the correct relation name.

Final Answer:
B is related to C as her Uncle.