The difference between nitrogen oxide (NO) and nitrogen dioxide (NO₂) lies primarily in the number of oxygen atoms in each molecule:

* Nitrogen Oxide (NO): Contains one nitrogen atom and one oxygen atom. It is a colorless gas at room temperature.

* Nitrogen Dioxide (NO₂): Contains one nitrogen atom and two oxygen atoms. It is a reddish-brown gas at room temperature.

Here's a breakdown of their key differences:

| Feature | Nitrogen Oxide (NO) | Nitrogen Dioxide (NO₂) |

|---|---|---|

| Chemical formula | NO | NO₂ |

| Appearance | Colorless gas | Reddish-brown gas |

| Toxicity | Toxic, but less toxic than NO₂ | Highly toxic |

| Role in air pollution | Contributes to smog formation | Primary component of acid rain |

| Health effects | Can cause headaches, dizziness, and respiratory problems | Can cause lung irritation, bronchitis, and asthma |

In addition to these differences:

* NO is relatively unreactive, but it can readily react with oxygen to form NO₂.

* NO₂ is a more reactive molecule and is a key component in the formation of acid rain and smog.

Overall, while both nitrogen oxide and nitrogen dioxide are pollutants, nitrogen dioxide is significantly more toxic and poses greater environmental risks.