Pick out the odd one from the following: $3,5,7,9,11,13,17,19$

Let's examine the numbers given in the series: $3,5,7,9,11,13,17,19$.
* $3,5,7,11,13,17,19$ are all prime numbers (numbers divisible only by $1$ and themselves).
* $9$ is a composite number since it has divisors other than $1$ and itself ($3\times 3=9$).

Therefore, $9$ is the odd one out.