Question

Of the species, $\mathrm{NO},{\mathrm{NO}}^{+},{\mathrm{NO}}^{2+}\mathrm{and}{\mathrm{NO}}^{-}$, the one with minimum bond strength is:

• A. ${\mathrm{NO}}^{-}$
• B. ${\mathrm{NO}}^{+}$
• C. ${\mathrm{NO}}^{2+}$
• D. $\mathrm{NO}$

Answer 1

The correct option is A

${\mathrm{NO}}^{-}$

Explanation for correct answer:-

Option (A) ${\mathrm{NO}}^{-}$:

• Bond strength can be defined as the strength with which two atoms are held together by a chemical bond.
• Lesser the distance between the two atoms greater will be the bond strength, or we can say that Bond strength is inversely proportional to the bond length.
• Ans we also know bond order is inversely proportional to the bond length $\mathrm{B}.\mathrm{O}\propto \frac{1}{\mathrm{B}.\mathrm{L}}$
• Thus we can say that the more the Bond order greater will be the bond strength.
• Bond order is calculated by the formula, $=\frac{1}{2}({\mathrm{N}}_{\mathrm{a}}-{\mathrm{N}}_{\mathrm{b}})$, here ${\mathrm{N}}_{\mathrm{a}}=$number of anti-bonding electrons, ${\mathrm{N}}_{\mathrm{b}}=$number of bonding electrons.
• Electronic configuration of ${\mathrm{NO}}^{-}$is $\mathrm{\sigma }1{\mathrm{s}}^2{\mathrm{\sigma }}^{\ast }1{\mathrm{s}}^2\mathrm{\sigma }2{\mathrm{s}}^2{\mathrm{\sigma }}^{\ast }2{\mathrm{s}}^2\mathrm{\sigma }2{\mathrm{p}}_{\mathrm{z}}^2\mathrm{\pi }2{\mathrm{p}}_{\mathrm{x}}^2\mathrm{\pi }2{\mathrm{p}}_{\mathrm{y}}^2{\mathrm{\pi }}^{\ast }2{\mathrm{p}}_{\mathrm{x}}^1{\mathrm{\pi }}^{\ast }2{\mathrm{p}}_{\mathrm{y}}^1$
• $\therefore$$$\begin{gathered} \mathrm{B}.\mathrm{O}.=\frac{1}{2}({\mathrm{N}}_{\mathrm{a}}-{\mathrm{N}}_{\mathrm{b}}) \\ \mathrm{B}.\mathrm{O}.=\frac{1}{2}(10-6) \\ \mathrm{B}.\mathrm{O}.=\frac{1}{2}\times 4 \\ \mathrm{B}.\mathrm{O}.=2 \end{gathered}$$
• Thus it is the lowest among the others, as a result, its bond strength is also the minimum
• Hence it is the correct option

Explanation for incorrect answer:-

Option (B) ${\mathrm{NO}}^{+}$:

• Electronic configuration of ${\mathrm{NO}}^{+}$is $\mathrm{\sigma }1{\mathrm{s}}^2{\mathrm{\sigma }}^{\ast }1{\mathrm{s}}^2\mathrm{\sigma }2{\mathrm{s}}^2{\mathrm{\sigma }}^{\ast }2{\mathrm{s}}^2\mathrm{\sigma }2{\mathrm{p}}_{\mathrm{z}}^2\mathrm{\pi }2{\mathrm{p}}_{\mathrm{x}}^2\mathrm{\pi }2{\mathrm{p}}_{\mathrm{y}}^2$
• $\therefore$$$\begin{gathered} \mathrm{B}.\mathrm{O}.=\frac{1}{2}({\mathrm{N}}_{\mathrm{a}}-{\mathrm{N}}_{\mathrm{b}}) \\ \mathrm{B}.\mathrm{O}.=\frac{1}{2}(10-4) \\ \mathrm{B}.\mathrm{O}.=\frac{1}{2}\times 6 \\ \mathrm{B}.\mathrm{O}.=3 \end{gathered}$$
• Thus it is not the lowest among the others, as a result, its bond strength is also not the minimum
• Hence it is the incorrect option

Option (C) ${\mathrm{NO}}^{2+}$:

• Electronic configuration of ${\mathrm{NO}}^{2+}$is $\mathrm{\sigma }1{\mathrm{s}}^2{\mathrm{\sigma }}^{\ast }1{\mathrm{s}}^2\mathrm{\sigma }2{\mathrm{s}}^2{\mathrm{\sigma }}^{\ast }2{\mathrm{s}}^2\mathrm{\sigma }2{\mathrm{p}}_{\mathrm{z}}^2\mathrm{\pi }2{\mathrm{p}}_{\mathrm{x}}^2{\mathrm{\pi }}^{\ast }2{\mathrm{p}}_{\mathrm{y}}^1$
• $\therefore$$$\begin{gathered} \mathrm{B}.\mathrm{O}.=\frac{1}{2}({\mathrm{N}}_{\mathrm{a}}-{\mathrm{N}}_{\mathrm{b}}) \\ \mathrm{B}.\mathrm{O}.=\frac{1}{2}(10-5) \\ \mathrm{B}.\mathrm{O}.=\frac{1}{2}\times 5 \\ \mathrm{B}.\mathrm{O}.=2.5 \end{gathered}$$
• Thus it is not the lowest among the others, as a result, its bond strength is also not the minimum
• Hence it is the incorrect option

Option (D) $\mathrm{NO}$:

• Electronic configuration of $\mathrm{NO}$is $\mathrm{\sigma }1{\mathrm{s}}^2{\mathrm{\sigma }}^{\ast }1{\mathrm{s}}^2\mathrm{\sigma }2{\mathrm{s}}^2{\mathrm{\sigma }}^{\ast }2{\mathrm{s}}^2\mathrm{\sigma }2{\mathrm{p}}_{\mathrm{z}}^2\mathrm{\pi }2{\mathrm{p}}_{\mathrm{x}}^2\mathrm{\pi }2{\mathrm{p}}_{\mathrm{y}}^2{\mathrm{\pi }}^{\ast }2{\mathrm{p}}_{\mathrm{x}}^1$
• $\therefore$$$\begin{gathered} \mathrm{B}.\mathrm{O}.=\frac{1}{2}({\mathrm{N}}_{\mathrm{a}}-{\mathrm{N}}_{\mathrm{b}}) \\ \mathrm{B}.\mathrm{O}.=\frac{1}{2}(10-5) \\ \mathrm{B}.\mathrm{O}.=\frac{1}{2}\times 5 \\ \mathrm{B}.\mathrm{O}.=2.5 \end{gathered}$$
• Thus it is not the lowest among the others, as a result, its bond strength is also not the minimum
• Hence it is the incorrect option

Therefore, Of the species, $\mathrm{NO},{\mathrm{NO}}^{+},{\mathrm{NO}}^{2+}\mathrm{and}{\mathrm{NO}}^{-}$, the one with minimum bond strength is option (A) ${\mathrm{NO}}^{-}$