What is the oxidation number of cl - in the perchlorate ion

The answer is: + 7

Explanation:

Oxidation state or oxidation number of an element is the hypothetical charge on an element that forms completely ionic bonds. The oxidation number represents the number of electrons lost or gained by that element.

Perchlorate ion is a molecule with a chemical formula: ClO₄⁻

The oxidation state of oxygen in ClO₄⁻ = - 2,

the total charge on the ClO₄⁻ molecule = - 1,

let the oxidation state of chlorine be x

As the sum of oxidation states of all elements in a molecule is equal to the total charge on the molecule.

⇒ oxidation state of chlorine + oxidation state of oxygen * 4 = total charge on the molecule

⇒ x + (-2) * 4 = - 1

⇒ x + (-8) = - 1

⇒ x = - 1 + 8 = + 7

⇒ x = + 7

Therefore, the oxidation state of chlorine in the perchlorate ion (ClO₄⁻) : x = + 7