Question

The oxidation state of N in $HN{O}_3$ is :
a.) +7
b.) +10
c.) +5
d.) +3

Answer 1

Hint: Since, clearly $HN{O}_3$ has overall neutral charge. That implies that the sum of oxidation numbers of all the elements present in the nitric acid will be zero. We can take the oxidation state of N in $HN{O}_3$as a variable “x” and add it to the oxidation states of Hydrogen and oxygen and then equate the sum to zero. We can use this approach for finding the solution to this question.

Complete answer:
Let us first recall what oxidation number is, and what are the rules we use to determine the oxidation number.
An oxidation state is defined to be a number that is given to an element in a chemical combination of a compound. This number represents the number of electrons that an atom may gain, lose, or share when it is chemically bonding with an atom of another element. The terms “oxidation state” and “oxidation number” are one and the same things. The transfer of electrons is often demonstrated by the oxidation state of the molecule.
Rules for determining the oxidation number
Oxidation numbers are usually written with a sign which can be a plus sign or a minus sign first, then the magnitude, which is the opposite of charges on ions. The following rules are kept in mind to write oxidation number -
Atoms present in their elemental state have an oxidation number of 0.
Atoms which are present in the monatomic (i.e. single atom) ions have an oxidation number equal to their charge respectively.
In a compound, the oxidation state for Group 1(1A) element is +1 and for Group 2(2A) element, the oxidation state is +2.
In compounds, all other atoms are assigned an oxidation number so that the sum of the oxidation numbers on all the atoms in the species equals the charge on the species.
The oxidation state of element Fluorine is -1 in a compound.
The oxidation state of element Hydrogen is +1 in a compound.
The oxidation state of element Oxygen is -2 in a compound.
In the two-element compounds with metals, Group 15(3A) elements have the oxidation state of -3, Group 16(6A) elements have the oxidation state of -2, and Group 17(7A) elements have the oxidation state of -1.
So now coming to the nitric acid given in the question –
If we let x be the oxidation number of N in nitric acid.
The oxidation numbers of H and O in nitric acid are +1 and −2 respectively as we have already specified the rules. Also because the sum of the oxidation numbers is zero for the neutral molecule it implies that -
1 + x + 3(-2) = 0
or, x=5

Therefore, Option (C) that is 5 is the correct answer.

Note: Oxidation is considered to be the loss of one or more electrons by an atom. Reduction is a term that is used to define the gain of one or more electrons by an atom.