Halogens react with air in a variety of ways, depending on the halogen and the conditions. In general, halogens are highly reactive and can form a variety of compounds with other elements.

At room temperature, halogens react with oxygen to form oxides. For example, chlorine gas reacts with oxygen to form chlorine monoxide (ClO) and chlorine dioxide (ClO2).

2Cl2(g) + O2(g) → 2ClO(g)

Cl2(g) + 2O2(g) → 2ClO2(g)

These oxides are corrosive and can cause a variety of health problems, including irritation of the eyes, nose, and throat.

At higher temperatures, halogens can also react with nitrogen to form nitrides. For example, fluorine gas reacts with nitrogen to form nitrogen trifluoride (NF3).

N2(g) + 3F2(g) → 2NF3(g)

Nitrides are often used as fertilizers and explosives.

In the presence of water, halogens can react to form acids. For example, chlorine gas reacts with water to form hydrochloric acid (HCl).

Cl2(g) + H2O(l) → 2HCl(aq)

Acids are corrosive and can cause a variety of health problems, including burns and irritation of the eyes, nose, and throat.

The reactivity of halogens decreases from fluorine to iodine. This is because the fluorine atom has the smallest atomic radius and the highest electronegativity of all the halogens. This means that fluorine atoms are more likely to attract electrons from other atoms, which makes them more reactive.