Pointing towards a girl, Chetan said, "She is the daughter of the only child of my grandmother." How is Chetan related to that girl?

Introduction / Context:
This question focuses on understanding phrases like only child of my grandmother and then taking the daughter of that person. You must carefully identify who the only child is, and then how their daughter is related to both the grandmother and to Chetan. Once that is clear, you can determine whether Chetan is a brother, father, husband or something else to the girl mentioned.

Given Data / Assumptions:
- Speaker: Chetan. - The girl being pointed at is the daughter of the only child of Chetan's grandmother. - The grandmother has exactly one child. - Chetan is a grandchild of that same grandmother. - We assume standard meanings for only child, daughter and grandmother.

Concept / Approach:
If Chetan's grandmother has only one child, then that single child must be either Chetan's father or Chetan's mother. There are no other children at that generation. The girl in question is the daughter of that only child, which makes her a child of Chetan's parent. Therefore, she must be one of Chetan's own siblings. Since the girl is explicitly described as female, the likely relationship between Chetan and the girl is that of brother and sister.

Step-by-Step Solution:
Step 1: Identify the only child of my grandmother. Because Chetan is a grandchild of this grandmother, her only child must be Chetan's parent. Step 2: The girl is the daughter of that only child. So she is the daughter of Chetan's parent. Step 3: Being a daughter of Chetan's parent makes the girl a child in the same generation as Chetan. In other words, she is Chetan's sister. Step 4: The question asks how Chetan is related to that girl. If the girl is his sister, and Chetan is male, then Chetan is her brother. Step 5: So the relation from Chetan to the girl is brother.

Verification / Alternative check:
Visualise a simple family tree: Grandmother at the top, one child in the next generation, and then two grandchildren in the next: Chetan and the girl. Both grandchildren share the same parent (the only child of the grandmother). In such a tree, the relationship between the two grandchildren is unmistakably brother and sister if one is male and the other is female. This confirms the conclusion.

Why Other Options Are Wrong:
- Father: For Chetan to be the girl's father, he would have to be a generation above her, which he is not; they share a parent instead. - Son: The question asks how Chetan is related to the girl, not how she is related to him. - Husband: That would imply they are married, which contradicts the sibling relationship derived from the common parent. - Uncle: An uncle would be the brother of the girl's parent, but Chetan is the child of that parent, not a sibling of the parent.

Common Pitfalls:
Many students get confused by the phrase only child of my grandmother and imagine some aunt or uncle, forgetting that the speaker himself must descend from that person if the grandmother has only one child. Another mistake is to lose track of generations and place Chetan one level too high or too low. Always ask: whose child is whose, and which generation does each person occupy.

Final Answer:
Chetan is the girl's brother.