Residue class rings of Z/Field/Integer/Prime number/Fact

Let $n\ge 1$ be a natural number, and let $\mathbb{Z}/(n)$ be the corresponding residue class ring.

Then the following statements are equivalent.

1. $\mathbb{Z}/(n)$ is a field.
2. $\mathbb{Z}/(n)$ is a domain.
3. $n$ is a prime number.

Write a proof