Answer:
The correct answer would be Y-chromosome analysis.
Y-chromosome analysis is technique used to search the parental line of a boy on his father's side.
Gender of a person is determined by chromosome in humans. XX is present in females and XY is present in males.
Mother always passes X chromosome to her progeny but father passes both X and Y chromosomes. If X is passed from the father then the offspring will be a girl and if Y is passed from the father then the offspring will be the son.
The sons (F₂) of this son (F₁) will also bear the same Y chromosome as that of grand father (P).
Thus, Y chromosome always passes from father to son and hence, Y-chromosome analysis can help in identification of father of this young boy.