Pointing towards a man, Ritika said, "He is the son of my grandfather's only son." How is Ritika related to that man?

Introduction / Context:
This question is centered around the phrase my grandfather's only son. When a person says my grandfather's only son, that person is normally referring to their father, because grandfather's only son is the only male child of the grandfather. The man pointed at is the son of that only son, so you must work out how Ritika is placed in the same family and what her relationship is to the man.

Given Data / Assumptions:
- Speaker: Ritika. - The man is the son of Ritika's grandfather's only son. - Ritika shares the same grandfather. - Only son means the grandfather has exactly one son. - We assume that this only son is Ritika's father (the standard exam assumption).

Concept / Approach:
If Ritika's grandfather has exactly one son, he must be the father of all grandchildren from his line, including Ritika. Thus, my grandfather's only son is Ritika's father. The man is then the son of Ritika's father, making him one of Ritika's siblings. If Ritika is female and the man is male, then the relationship between Ritika and the man is that of sister and brother, specifically Ritika being the sister of the man.

Step-by-Step Solution:
Step 1: Interpret grandfather's only son. Since Ritika is a grandchild, her grandfather's only son is her father. Step 2: The man is described as the son of that only son. So the man is the son of Ritika's father. Step 3: Children of the same father (and typically the same mother in these puzzles) are siblings to one another. Step 4: Ritika is female and the man is male, and both are children of the same father. Thus, Ritika is the man's sister. Step 5: Therefore, Ritika is related to the man as his sister.

Verification / Alternative check:
Draw a small family tree: Grandfather at the top, his only son (Ritika's father) below. Under the father, place his children: Ritika and the man. From the perspective of either child, the other is a sibling. Specifically, since Ritika is a girl and the other is a boy, he is her brother and she is his sister. This confirms the verbal reasoning.

Why Other Options Are Wrong:
- Aunt: Ritika would be an aunt only to the children of her sibling, not to the sibling himself. - Mother: Being the sister of the man does not make her his mother; they are of the same generation. - Wife: Spouses typically come from different families or at least are not immediate siblings; this would violate standard family norms in such questions. - Cousin: Cousins share grandparents, but they are children of different parents. Here, both are children of the same father.

Common Pitfalls:
A common error is to confuse grandfather's son with uncle. In this puzzle, the phrase only son is critical: if the grandfather has only one son, that son must be the father of the speaker, not an uncle. Another pitfall is ignoring the gender of the speaker and the pointed person, which helps determine whether the answer is brother or sister from the speaker's viewpoint. The question explicitly asks how Ritika is related to the man, so the correct phrasing is sister.

Final Answer:
Ritika is the man's sister.