Out of the different oxides of nitrogen, which of the following are considered as air pollutants and known as NOx?

Nitric oxide, Statement 1, and nitrogen dioxide, Statement 2, together make up the reactive NOx group of air pollutants.

Nitric oxide forms in high-temperature combustion and oxidises in air to nitrogen dioxide.

Nitrogen trioxide, Statement 3, is an unstable radical and is not part of the regulatory NOx category.

Nitrous oxide, Statement 4, is a potent greenhouse gas but chemically inert and not classed as NOx.

Only Statements 1 and 2 belong to NOx, while Statements 3 and 4 do not.

NOx forms mainly during high-temperature burning in engines and power plants and drives smog and acid rain.