Question

The species having bond order different from that in CO is
(A)$N{O^ - }$
(B)$N{O^ + }$
(C)$C{N^ - }$
(D)${N_2}$

Answer 1

Hint: Bond order is defined as the half of the difference between the bonding and antibonding electrons. The species having the same number of electrons are called isoelectronic species. Also, the isoelectronic species are having the same bond order.

Complete step by step solution: We have been given four different species out of which we have to find the one whose bond order is different from that in carbon monoxide.
We have been given a CO molecule which contains fourteen electrons. We will write the bond order of this molecule. The electronic configuration is given as follows
CO$ = \sigma 1{s^2}{\sigma ^*}1{s^2}\sigma 2{s^2}\pi 2p_x^2 \approx \pi 2p_y^2\sigma 2p_z^2$
Now BO$ = \dfrac{1}{2}({N_B} - {N_A})$
Where BO is the bond order and ${N_B}$,${N_A}$ are the number of electrons in bonding and antibonding orbitals respectively.
$ \Rightarrow $BO$ = \dfrac{{10 - 4}}{2} = 3$
Now for $N{O^ - }$ the bond order is given as follows. The electronic configuration $N{O^ - }$ is given as follows
It is having sixteen electrons so the electronic configuration is as follows
$N{O^ - }$$ = \sigma 1{s^2}\sigma 2{s^2}{\sigma ^*}2{s^2}\sigma 2p_z^2\pi 2p_x^2 \approx \pi 2p_y^2{\pi ^*}2p_x^1 \approx {\pi ^*}2p_y^1$
Now BO$ = \dfrac{1}{2}({N_B} - {N_A})$
$ \Rightarrow $BO$ = \dfrac{{10 - 6}}{2} = 2$
Now $N{O^ + }$ is having the same number of electrons and has the same bond order as that of CO.
i.e.BO$ = 3$
Now cyanide ion($C{N^ - }$) is having fourteen electrons and having the same bond order.
i.e.$BO = 3$
Also, nitrogen molecules (${N_2}$) have fourteen electrons and have the same bond order.
i.e. BO$ = 3$
Therefore $N{O^ + },C{N^ - },{N_2}$ is having the same bond order as CO and $N{O^ - }$ has a different bond order compared to CO.

Hence, the correct answer is option A.

Note: Other than the isoelectronic species concept we can solve this problem by manually calculating the bond order of every species and then compare it with the bond order of CO to get the correct answer. Bond order in isoelectronic species is the same as bond order depends on the number of electrons in bonding and antibonding orbitals. Isoelectronic species have the same number of electrons and hence same bond order.