| RollNo | Name | Mobile | City |
| 1 | Arun | 91 | Delhi |
| 2 | Sanjay | 92 | Mumbai |
| 3 | Arun | 93 | Noida |
| 4 | Varun | 94 | Guwahati |
| 5 | Arti | 95 | Kolkata |
The objective is to determine the count of candidate keys within the presented table. A candidate key is defined as the smallest collection of attributes capable of uniquely identifying a record in a table. Analyzing 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 |
'RollNo' is unique for each student, thus qualifying as a candidate key.
'Mobile' numbers are also unique, making them a candidate key as well.
Based on this evaluation, there are two candidate keys: 'RollNo' and 'Mobile'.
Consequently, the answer is: Two.
| List-I | List-II |
| (A) Controlled Data Sharing | (I) Same data maintained in different places does not match |
| (B) Data Isolation | (II) Limited Access given to users |
| (C) Data Dependence | (III) There is no mapping between two files |
| (D) Data Inconsistency | (IV) If the structure of a file is changed, all the existing programs accessing that file also need to be changed |