Question

How many candidate keys are possible with the table?

RollNo	Name	Mobile	City
1	Arun	91	Delhi
2	Sanjay	92	Mumbai
3	Arun	93	Noida
4	Varun	94	Guwahati
5	Arti	95	Kolkata

• A. One
• B. Two
• C. Three
• D. Four

Answer 1

The Correct Option is B

In the provided table, we need to identify the number of candidate keys. A candidate key is defined as a minimal set of attributes that can uniquely identify a table record. Let's analyze the table: 

RollNo	Name	Mobile	City
1	Arun	91	Delhi
2	Sanjay	92	Mumbai
3	Arun	93	Noida
4	Varun	94	Guwahati
5	Arti	95	Kolkata

Each 'RollNo' is unique for every student, hence it can be a candidate key.

Each 'Mobile' number is also unique, thus it can be a candidate key.

Considering this analysis, we have two candidate keys: 'RollNo' and 'Mobile'.

Therefore, the correct answer is: Two.

Answer 2

A candidate key is a minimal set of attributes that uniquely identifies each tuple in a table.

In the given table:

Therefore, the candidate keys are RollNo and Mobile.

Thus, the answer is (2) Two.