Pointing to Ketan, Namrata said, 'He is the son of my father's only son'. How is Ketan's mother related to Namrata?

Explanation Option [d] is correct. Namrata's father's only son- Namrata's Brother. So, Ketan is the son of Namrata's Brother. Thus, Ketan's mother is the wife of Namrata's brother i.e. Namrata's sister-in-law. Rest of the options is incorrect because of the correctness of option [d].