Four diatomic species are listed in different sequence .Which of these represent the correct order of their increasing bond order?

Options

A. `O_2^(-) lt NO lt C_2^(2-) lt He_2^+`
B. `NO lt C_2^(2-) lt O_2^(-) lt He_2^(+)`
C. `C_2^(2-) lt He_2^(+) lt NO lt O_2^(-)`
D. `He_2^(+) lt O_2^(-) lt NO lt C_2^(2-)`

Answer

D

Explanation

The molecular orbital configuration of
`O_2^-` (8+8+1=17)=`sigma1s^2,overset***sigma1s^2,sigma2s^2,overset***sigma2s^2,sigma2p_x^2,pi2p_y^2~~pi2p_z^2,overset***2p_y^2~~overset***pi2p_z^1`
Bond order (BO)=`(N_b-N_a)/2=(10-7)/2=1.5`
`NO` (7+8=15)=`sigma1s^2,overset***sigma1s^2,sigma2s^2,overset***sigma2s^2,sigma2p_x^2,pi2p_y^1~~pi2p_z^0`
Bond order (BO)=`(10-5)/2=2.5`
`C_2^(2-)` (6+6+2=14)=`sigma1s^2,overset***sigma1s^2,sigma2s^2,overset***sigma2s^2,pi2p_y^2~~pi2p_z^2,overset***2p_x^2`
Bond order (BO)=`(10-4)/2=3`
`He_2^+` (2+2-1=3) =`sigma1s^2, overset***1s^1`
BO`=(2-1)/2=1/2=0.5`
Hence, order of increasing bond order is
`He_2^(+) lt O_2^(-) lt NO lt C_2^(2-)`