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Consider the following functional dependencies in a database.

 Date_of_Birth $\to$ Age Age $\to$ Eligibility Name $\to$ Roll_number Roll_number $\to$ Name Course_number $\to$ Course_name Course_number $\to$ Instructor (Roll_number, Course_number) $\to$ Grade

The relation (Roll_number, Name, Date_of_birth, Age) is

1. in second normal form but not in third normal form
2. in third normal form but not in BCNF
3. in BCNF
4. in none of the above

There are three FDs that are valid from the above set of FDs for the given relation :

Date_of_Birth $\to$ Age

Name $\to$ Roll_number

Roll_number $\to$ Name

Candidate keys for the above are : (Date_of_Birth,Name) and (Date_of_Birth, Roll_number)

Clearly there is partial dependency here (Date_of_Birth $\to$ Age) and Age is not a prime attribute. So, it is only in 1NF.

Option (D).
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There are also given two other fds  i.e course no ,course name and instructor.for the ck all fds should be derived from it
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@Neha Singh we need to find dependency btw given relation only which is The relation (Roll_number, Name, Date_of_birth, Age) so all extra dependency other than relation no use
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Prateek kumar but there may be other fd that can be indirectly derived from the attribute not present in the table thus it is always advisable to find all the possible fd's by using the closure method and see which are applicable to the given relation .

there is partial dependency hence it is 1st normal form