Question

what is the formula for knowing the oxidation number of a element

Answer 1

The oxidation number of a free element is always 0. The oxidation numberof a monatomic ion equals thecharge of the ion. The oxidation number of H is +1, but it is -1 in when combined with less electronegative elements. Theoxidation number of O in compounds is usually -2, but it is -1 in peroxides.

Answer 2

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The oxidation number of a Group 2 element in a compound is +2. The oxidation number of a Group 17 element in a binary compound is -1. The sum of the oxidation numbers of all of the atoms in a neutral compound is 0. The sum of the oxidation numbers in a polyatomic ion is equal to the charge of the ion.