All of the following elements will form ions by gaining

electrons, except

iodine

magnesium

sulfur

phosphorus

Magnesium

Explanation:

When an atom loses are gain the electrons ions are formed.

There are two types of ions.

Anion

Cation

1 = Anion

It is formed when an atom gain the electrons. when atom gain electron negative charge is created on atom. For example.

X + e⁻ → X⁻

2 = Cation

It is formed when an atom loses the electrons. when atom lose electron positive charge is created on atom. For example.

X → X⁺ + e⁻

There are seven valance electrons in iodine. To complete the octet it gain one electron and form anion.

Sulfur has six valance electrons it gain two electrons to complete the octet and form anion.

Phosphorus has five valance electrons it gain three electrons two complete the octet and form anion.

Magnesium has two valance electrons it loses two electron to complete the octet and form cation.