Question
Which one of the following constitutes a group of the isoelectronic species?
A.
$$C_2^{2 - },O_2^ - ,CO,NO$$
B.
$$N{O^ + },C_2^{2 - },C{N^ - },{N_2}$$
C.
$$C{N^ - },{N_2},O_2^{2 - },C_2^{2 - }$$
D.
$${N_2},O_2^ - ,N{O^ + },CO$$
Answer :
$$N{O^ + },C_2^{2 - },C{N^ - },{N_2}$$
Solution :
Species having same number of electrons are isoelectronic calculating the number of electrons in each species given here, we get.
$$\eqalign{
& C{N^ - }\left( {6 + 7 + 1 = 14} \right);\,{N_2}\left( {7 + 7 = 14} \right); \cr
& O_2^{2 - }\left( {8 + 8 + 2 = 18} \right);\,C_2^{2 - }\left( {6 + 6 + 2 = 14} \right); \cr
& O_2^ - \left( {8 + 8 + 1 = 17} \right);\,N{O^ + }\left( {7 + 8 - 1 = 14} \right) \cr
& CO\left( {6 + 8 = 14} \right);\,NO\left( {7 + 8 = 15} \right) \cr} $$
From the above calculation we find that all the species listed in choice (B) have 14 electrons each so it is the correct answer.