Blood relations – precise identification: Pointing to a boy, Sumita said, "He is the son of my grandfather's only son." How is the boy related to Sumita?

Introduction / Context:
This problem tests core kinship translation. We convert a layered description ("my grandfather's only son") into a direct relation with the speaker (Sumita) and then determine how that person's son relates to her.

Given Data / Assumptions:

• Speaker: Sumita (female).
• "My grandfather's only son" refers to the sole male child of Sumita's grandfather.
• Standard, monogenerational family tree; no adoption/step-relations implied unless stated.

Concept / Approach:
First decode "my grandfather's only son." Sumita's grandfather's only son is Sumita's father. Then the boy in question is "the son of my father," i.e., a male child of her father. Children of the same father (and mother unless otherwise noted) are siblings; since the child is male, he is Sumita's brother.

Step-by-Step Solution:

Verification / Alternative check:
If the only son were an uncle, Sumita's parent would not be that person. But "only son" leaves no other male child—so it must be her father (otherwise Sumita would have no father or the description would contradict "only"). Hence the boy is necessarily her brother.

Why Other Options Are Wrong:
Nephew/Cousin/Uncle imply different generations/branches; Son would require Sumita to be the boy's mother, which is not stated or implied.

Common Pitfalls:
Confusing "grandfather's only son" with "father's only son" or misplacing the generational step.

Final Answer:
Brother