Problem question: Who is Jill's uncle? Statements: I) Jill's father Bill's…

CONCEPT: In a data-sufficiency family-relation question, a single statement is SUFFICIENT only if, read entirely on its own, it pins down one unambiguous answer to the exact relation asked. If a statement's own wording allows more than one possible person, or never links its chain back to the side of the family being asked about, it is INSUFFICIENT — the governing rule is that an ambiguous statement counts as insufficient, not as 'maybe sufficient'.

APPLICATION — Statement I: Bill is Jill's father, and Jack is named as Bill's ONLY nephew, so Jack is the son of one of Bill's siblings. The same statement adds that Jack is Sam's son, i.e. Sam is Jack's father. Whichever sibling of Bill is Jack's parent, Sam turns out to be either Bill's brother directly, or the husband of Bill's sister — and relative to Jill (Bill's child) both of those people are Jill's uncle. So Statement I on its own fixes a single answer: Sam is Jill's uncle. It is sufficient.

APPLICATION — Statement II: Frank is reached through a long chain — Jill's only paternal cousin's maternal aunt's only brother-in-law. This never pins Frank to one definite position relative to Bill's family: 'brother-in-law' itself carries two everyday senses (a woman's husband's brother, or her own sister's husband), and the two senses point to different people, at most one of whom lies on Jill's father's side. Because the statement's own wording never settles which person Frank is, it does not deliver a unique answer to 'who is Jill's uncle', so on its own it is insufficient.

CROSS-CHECK: Statement I yields exactly one identification (Sam) with no competing reading, whereas Statement II fails to converge on any single person at all. Therefore Statement I alone answers the question while Statement II alone does not — the correct verdict is that Statement I alone is sufficient.