Introducing a girl, Poonam says, "She is the daughter of the only sister of the son of my mother." How is that girl related to Poonam?

Introduction / Context:

This blood-relation puzzle involves a layered description: "the only sister of the son of my mother". The trick is to simplify this expression step by step, replacing each part with clear relationships to Poonam. Such questions are common in reasoning sections because they practice your ability to follow chains like mother → son → sister and then determine the final relationship.

Given Data / Assumptions:

• Poonam is speaking.
• She introduces a girl and says: "She is the daughter of the only sister of the son of my mother."
• "My mother" refers to Poonam's own mother.
• "The son of my mother" refers to Poonam's brother (a male child of her mother).
• "The only sister" of that son must be Poonam herself, because she is female and the only sister mentioned.
• The girl is the daughter of that "only sister".
• We need to find how the girl is related to Poonam.

Concept / Approach:

The key insight is that the phrase "only sister of the son of my mother" circles back to Poonam herself. Once that is recognized, the remaining phrase "daughter of that sister" simplifies to "my daughter". Therefore, the girl is Poonam's own daughter. The options contain several tempting distractors like niece and cousin, but they do not match the precise logical chain.

Step-by-Step Solution:

Verification / Alternative check:

We can test the logic with a concrete example. Suppose Poonam's mother has exactly two children: a son Raj and a daughter Poonam. Raj's only sister is Poonam. If Poonam now has a daughter Riya, Riya can be described precisely as "the daughter of the only sister of the son of my mother". This is exactly the sentence Poonam uses. From Poonam's point of view, Riya is her daughter, and this matches our reasoning.

Why Other Options Are Wrong:

"Niece" would be correct if the girl were the daughter of Poonam's sibling. Here she is the daughter of Poonam herself, not of her brother.

"Cousin" would imply that the girl is a child of Poonam's aunt or uncle, which does not follow from the given description.

"Sister-in-law" is an in-law relation and is completely unrelated to the given generational chain involving "daughter" and "sister".

Common Pitfalls:

Some students mistakenly treat "the son of my mother" as someone other than the obvious brother, or they forget that "the only sister" must be the speaker herself. It helps to mentally replace phrases with simpler words: "my mother's son" = "my brother", and "my brother's only sister" = "me". Writing this clearly on paper can prevent confusion and incorrect answers like niece or cousin.

Final Answer:

The girl introduced by Poonam is her own daughter.