Pointing to a photograph, Vipul said, "She is the daughter of my grandfather's only son." How is Vipul related to the girl in the photograph

Instruction : In each of the following questions, there is some relationship between the two terms to left of:: and the Same relationship continues between the two terms to its right. Also in each question, one term either To the right of:: or to the left of it is missing. This term is given as one of the alternatives given below Each question. Find out the missing term.