The sum of the oxidation states of the individual atoms should be equal to the the net charge of the compound /ion.
Molecular formula of iron(III) hypochlorite is Fe(ClO)₃
This is made of a cation and anion. Cation is Fe³⁺ and anion is hypochlorite ion - ClO⁻
the net charge of the ion is -1
oxidation state of Cl - x and oxidation state of O - -2
x + (-2) = -1
x - 2 = -1
x = -1 + 2
x = +1
Therefore oxidation state of Cl is +1
