Select odd one out from the following and justify your answer.
He, Ar, CO, Ne

Explanation

To solve the question of selecting the odd one out from the list of gases: He (Helium), Ar (Argon), CO (Carbon Monoxide), and Ne (Neon), we can follow these steps:

### Step 1: Identify the types of gases
- **He (Helium)**: This is a noble gas and is monoatomic.
- **Ar (Argon)**: This is also a noble gas and is monoatomic.
- **CO (Carbon Monoxide)**: This is a compound and is diatomic.
- **Ne (Neon)**: This is another noble gas and is monoatomic.

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