The only attribute values permitted by 1 NF are single atomic (or indivisible) values. If there is no value present for the column, then it should be denoted as null.

Example to understand 1NF

Lets take an example for the following table data named as Student.

This table is not in First Normal Form because field Telephone_No containing more than one value. Also the first record is not having any values. To make the table in the first normal form we need to split the A103 rows into two and supply the blank value with null. So the resultant table is as follows:-