List three halogens, and describe a property
that they all share

Three halogens:

Fluorine, chlorine, bromine.

Explanation:

Halogens are present in group seventeen of periodic table.

Their are five elements in this group fluorine, chlorine, bromine, iodine, astatine.

Three halogens:

Fluorine, chlorine, bromine.

All these share common properties such as,

All of these have seven valance electrons.

When combine with hydrogen they form acids.

H₂ + Cl₂  → 2HCl

All of these are toxic in nature.

They are highly electronegative and most reactive elements.

When combine with metals they form salts such as sodium chloride, magnesium bromide.

2Na + Cl₂  →  2NaCl

2Na + Br₂ →  2NaBr

Mg + Br₂  → MgBr₂

Mg + Cl₂ → MgCl₂