In HClO₄ (perchloric acid), the oxidation number of chlorine (Cl) can be determined by considering the known oxidation states of the other elements and the overall charge of the compound.
First, let's assign the oxidation state of hydrogen (H) as +1 since it usually exhibits a +1 oxidation state in compounds.
Oxygen (O) is typically assigned an oxidation state of -2 in compounds, except in peroxides (where it is -1) or when bonded to fluorine (where it can be positive).
The overall charge of perchloric acid (HClO₄) is 0 since it is a neutral compound.
Now, we can calculate the oxidation state of chlorine (Cl):
Let x be the oxidation state of Cl. The sum of the oxidation states must equal 0: (+1) + x + 4(-2) = 0
Simplifying the equation: +1 + x - 8 = 0 x - 7 = 0 x = +7
Therefore, the oxidation number of chlorine (Cl) in HClO₄ is +7.