Answer
False
Work Step by Step
An irrational number is a number that cannot be expressed as a quotient of two integers.
Note that $9 = \frac{18}{2}$.
18 and 2 are integers.
Thus, $9$ is a rational number.
$\in$ means the number is an element of the given set.
Since $9$ is a rational number, it is not an irrational number.
Therefore, the given statement is false.
