Dhwani said, “This boy is the husband of the granddaughter of my father”. How is Dhwani related to the boy?

Let's break down the statement spoken by Dhwani:
1. "My father's granddaughter": This means either Dhwani's own daughter or Dhwani's sibling's daughter.
2. "The husband of the granddaughter": The boy is the husband of that granddaughter.

Let's examine the choices provided:

* If the granddaughter is Dhwani's own daughter, Dhwani becomes the Mother-in-law of the boy.
* If the granddaughter is Dhwani's brother's/sister's daughter, Dhwani would be an aunt-in-law.

Looking at the options, Mother-in-law ($\text{स्रास}$) is clearly listed as Option D. Thus, Dhwani is the mother-in-law of the boy.