The correct answer is (a) 8 years.
Under the Hindu Adoption and Maintenance Act, 1956, a child to be adopted should not have, in the absence of a valid custom, completed the age of 8 years. This means that the child must be under the age of 8 at the time of the adoption.
There are a few exceptions to this rule. For example, if the child is a Hindu by religion and has been abandoned by his or her parents, he or she may be adopted even if he or she is over the age of 8. Additionally, if the child is a Hindu by religion and has been orphaned, he or she may be adopted even if he or she is over the age of 8.
The purpose of this rule is to protect the rights of children. By limiting the age of adoption to 8 years, the law ensures that children are not adopted by people who may not have their best interests at heart. Additionally, the law helps to ensure that children are adopted into families that can provide them with the love and support they need.
The other options are incorrect because they are not the maximum age limit for adoption under the Hindu Adoption and Maintenance Act, 1956.