Question

What is the oxidation number of chlorine in $ClO_3^ -$?
A) +5
B) +3
C) +4
D) +2

Answer 1

oxidation number of an element may be defined as the charge which an atom of the element has in its ion or appears to have when present in the combined state with other atoms. The oxidation number is also known as the oxidation state.

Complete step by step answer:
There are the various rule for assigning the oxidation number, by using these rule we will find the oxidation number of $Cl$ in $ClO_3^ -$
As we know the oxidation number of oxygen is -2 in most of its compounds except in peroxide like hydrogen peroxide.
So assume the oxidation state of $Cl$ is x and the sum of the oxidation number of various atoms in $ClO_3^ -$ is
$x + ( - 2) \times 3 = - 1 \\\ \Rightarrow x - 6 = - 1 \\\ \Rightarrow x = - 1 + 6 \\\ \Rightarrow x = 5 \\\$
Hence the oxidation number $ClO_3^ -$ is 5.

Hence the correct answer is option A .

Additional Information:
Metals invariably have a positive oxidation state while non-metal has a positive or negative oxidation state. Transition metals usually display a variable oxidation state.
In the case of an s block element, the highest positive oxidation state is equal to group number and in the case of p block elements, it is equal to group number minus 10 (except in noble gas). The highest negative oxidation state of a p block element is equal to eight minus the number of valence electrons. In other words, we can say the highest positive oxidation state increases across a period in the periodic table.

Note:
In reality, no element can have a fractional oxidation state but in a compound, the same element exists in two different oxidation states, then the average oxidation state may be fractional value.