Explanation:

Let’s break down the statement step by step:

- "My father's mother" = Raghav's grandmother

- "Grandmother's daughter" = Raghav's father's sister (Raghav's aunt)

- "Aunt's only brother" = Raghav's father (since Raghav is a boy, the father's only brother is himself)

- "Father's daughter" = Raghav's sister

So the girl in the photograph is Raghav's sister.

Now, the question is:

How is Raghav’s father related to *that girl’s mother* (i.e., Raghav’s mother)?

- Raghav’s father is the husband of Raghav’s mother.

Let’s match with the options:

1. Son

2. Maternal uncle

3. Husband

4. Father

Option 3 (Husband) is the correct answer.