Answer:
The correct options are 1, 3 and 4.
Step-by-step explanation:
We need to find the expressions whose simplified form is a rational number.
Rational number: If a number is defined in the form of p/q where p and q are integers and q≠0, then it is called a rational number.
For example: 0,2, 4.3 etc.
Irrational number: If a number can not defined in the form of p/q, where p and q are integers and q≠0, then it is called an irrational number.
First expression is
12 is a rational number.
Second expression is
is an irrational number.
Third expression is
21 is a rational number.
Fourth expression is
5 is a rational number.
Therefore, the correct options are 1, 3 and 4.