7. Redox reactions — Chemistry STD 11 Science — Question

Consider the given reaction. The total number of oxygen atoms present per molecule of the product $(P)$ is___________

$\left. \begin{gathered}
  {\text{4N}}{{\text{H}}_{3(g)}}{\text{ + 5}}{{\text{O}}_{2(g)}} \to {\text{ 4N}}{{\text{O}}_{(g)}}{\text{ +  6}}{{\text{H}}_{\text{2}}}{{\text{O}}_{{\text{(l)}}}} \hfill \\
  {\text{2N}}{{\text{O}}_{(g)}}{\text{ + }}{{\text{O}}_{2(g)}} \to {\text{2N}}{{\text{O}}_{2(g)}} \hfill \\
  {\text{3N}}{{\text{O}}_{2(g)}}{\text{ +  }}{{\text{H}}_{{\text{ 2}}}}{{\text{O}}_{(l)}} \to {\text{2H N}}{{\text{O}}_{3(aq)}}{\text{ +  N}}{{\text{O}}_{(g)}} \hfill \\ 
\end{gathered}  \right|\begin{array}{*{20}{c}}
  {\Delta H(kJ)} \\ 
  { - 904} \\ 
  { - 112} \\ 
  { - 140} 
\end{array}$

Assertion ($A$): Enthalpy of neutralisation of strong monobasic acid with strong monoacidic base is always $-57 \mathrm{~kJ} \mathrm{~mol}^{-1}$

Reason ($R$): Enthalpy of neutralisation is the amount of heat liberated when one mole of $\mathrm{H}^{+}$ions furnished by acid combine with one mole of ${ }^{-} \mathrm{OH}$ ions furnished by base to form one mole of water. In the light of the above statements, choose the correct answer from the options given below.