Option (1) is correct: Under Section 10 of Hindu Adoptions and Maintenance Act,a person can be adopted if he is a Hindu.
Option (2) is incorrect: Under Section 10 of Hindu Adoptions and Maintenance Act,a person can be adopted if he is unmarried.
Option (3) is incorrect: Under Section 10 of Hindu Adoptions and Maintenance Act,a person cannot be adopted if he is above fifteen years of age.
Option (4) is incorrect: Under Section 10 of Hindu Adoptions and Maintenance Act,a person can be adopted if he is not already adopted.