Which of the following values cannot be stored in a character column defined as the primary key of a
table?

A.
null

B.
‘0’

C.
‘null’

D.
”

Explanation:
A primary key must be defined as NOT NULL. For a character column, any value, even a space, or lack
of a space, is a valid value. So the strings ”, ‘null’, and ‘0’ are valid strings and would be accepted as
input into a column that is a primary key. The value null is not acceptable.