Question

Which gas is evolved when $Pb{O_2}$ is treated with conc. $HN{O_3}$?
A: $N{O_2}$
B: ${O_2}$
C: ${N_2}$
D: ${N_2}O$

Answer 1

$Pb{O_2}$ is lead oxide. This compound is black in color and insoluble in water. This compound is a powerful oxidizing agent. $HN{O_3}$ is nitric acid. This compound is yellow in color due to the presence of oxides of nitrogen.

Complete step by step answer:
In this question we have to find the gas which is evolved when $Pb{O_2}$ is treated with conc. $HN{O_3}$. $Pb{O_2}$ is lead oxide. Possible oxidation states of lead are $+ 2$ and $+ 4$. Oxidation state is defined as a charge which is present on an atom if the compound was ionic. Oxidation state of one atom of oxygen is $- 2$ but in this compound two atoms of oxygen are present. So, the oxidation state of oxygen atoms will be $- 4$. As a whole, lead oxide is neutral this means charge on the compound is zero. Therefore charge on lead will be $+ 4$. Maximum oxidation state of lead is $+ 4$ this means lead can’t lose more electrons but it can gain electrons. When an atom gains electrons it is said to be reduced. This means lead will undergo reduction in this reaction. Reaction that will take place is written below:
$Pb{O_2} + conc.HN{O_3}\xrightarrow[{}]{}Pb{\left( {N{O_3}} \right)_2} + {H_2}O + {O_2}$

So, the correct answer is Option B.

Note:
The substance that itself undergoes reduction and oxidizes other in a chemical reaction is called an oxidizing agent. Whereas the substance that itself undergoes oxidation and reduces others in a chemical reaction is known as reducing agent. Oxidizing agent itself undergoes reduction and reducing agent itself undergoes oxidation.