Final answer:
In the context of a database, a key is used to uniquely identify a record. For the given attributes - Name, Age, Address, and Phone Number, the Phone Number is most likely to serve as a unique key assuming each individual has a unique phone number.
Step-by-step explanation:
Selecting the set of attributes that is a key for a database involves identifying a combination of fields that can uniquely identify a record within a database table. A key is a field or combination of fields that uniquely identifies a record. Common keys include a single field, like a Social Security Number for a person, or a composite key, which is made up of two or more fields.
Given the attributes of Name, Age, Address, and Phone Number, the most likely candidate for a unique identifier would be the Phone Number. This is because names can be shared by multiple individuals, ages are not unique and change every year, and addresses could potentially have more than one occupant. Phone numbers, on the other hand, are typically unique to each individual or household and therefore serve as a better key. However, without knowing the context of the database (such as whether phone numbers can have multiple users or if individuals can have multiple phone numbers), there is a potential for duplicates or complications. Ideally, databases should use a system-generated unique identifier as a key, like a customer ID.