Question

What is the oxidation number of Mn in $KMn{O_4}$?
A. -7
B. -3
C. 0
D. +3
E. +7

Answer 1

Hint: The unknown oxidation number of any metal can be found if the oxidation numbers of all the other constituents of a compound are known and the overall charge of the molecule is also known.

Complete step by step answer:
Potassium permanganate is an inorganic compound which has the chemical formula $KMn{O_4}$. It is composed of one ${K^ + }$ ion and one $Mn{O_4}^ -$ ion. It was first developed as a disinfectant in 1857. Since then, it’s been widely used to treat a variety of skin conditions, including fungal infections. Potassium permanganate is widely used in the chemical industry and laboratories as a strong oxidising agent.
In potassium permanganate, the potassium ions have a +1 oxidation state and the oxygen anions have a -2 oxidation state. The overall charge of the molecule is 0, i.e. the molecule is neutral. Let the oxidation state of manganese be ‘x’. Thus, we have an equation:
1 + x + 4(-2) = 0
∴ x = +7

Hence, the correct answer is (E) +7.

Note: Remember that the maximum oxidation number of manganese is +7, i.e. in potassium permanganate. The minimum oxidation state of manganese is -3. Manganese also acts as a self indicator in its titration reactions.