Pointing towards a boy, a girl says, "He is the only son of my mother brother." How is the girl related to the boy?

Introduction / Context:
This is a very standard blood relation question built around the idea of a maternal uncle. The girl points to a boy and describes him as the only son of her mother brother. From this description you must determine how she is related to the boy. These kinds of questions appear frequently in reasoning tests.

Given Data / Assumptions:

• A girl is pointing at a boy.
• She says, "He is the only son of my mother brother."
• "My mother brother" is the girl maternal uncle.
• The boy is the only son of that maternal uncle.
• We assume a normal family where children of siblings are cousins.

Concept / Approach:
The central idea is to recognise that "my mother brother" is your maternal uncle, and the son of your maternal uncle is your cousin. The girl who is speaking is the daughter of the uncle sister. The boy is the son of that uncle. Therefore they are children of siblings and hence first cousins.

Step-by-Step Solution:
Step 1: Identify the relative described by "my mother brother". He is the brother of the girl mother and is therefore the girl maternal uncle.Step 2: The boy is the only son of this maternal uncle. So the boy is the uncle son.Step 3: The girl herself is the daughter of the uncle sister, namely her mother.Step 4: Thus, the girl mother and the boy father are siblings.Step 5: Children of siblings are first cousins to each other.Step 6: Therefore, the girl and the boy are cousins, and from the girl side she is the cousin sister of the boy.

Verification / Alternative check:
Imagine names. Let the girl mother be Meera and her brother be Suresh. Suresh is the girl maternal uncle. If Suresh has one son named Rohan, then Rohan is the only son of Meera brother. The girl is Meera daughter. Since Meera and Suresh are siblings, their children are cousins. That means the girl is a cousin of Rohan. This matches the reasoning above.

Why Other Options Are Wrong:
The girl is not the boy grandmother or mother because they are in the same generation, not separated by a generation gap. She is not his aunt, because an aunt would be a sister of one of his parents, not a child of his parent sibling. The only correct same-generation relationship formed by children of siblings is cousin.

Common Pitfalls:
Some learners confuse the roles and think the girl could be an aunt if they misread "my mother brother" as "my brother mother". Careful reading is important. Another mistake is to think that only sons or only daughters change the basic cousin relationship, but the number of children does not change the fundamental type of relation between generations.

Final Answer:
The girl is related to the boy as his cousin.