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

Electronic configuration are
`He_2^(2+): (sigma1s)^2(sigma^**1s)^1`, `bo=(2-1)/(2)=1/2=0.5`
`O_2^(-):KK(sigma2s)^2(sigma^**2s)^2(sigma2p_z)^2(pi2p_x^2=pi2p_y^2)(pi^**2p_x^2=pi^**2p_y^1)`
`bo=(10-7)/(2)=1.5`
`NO:KK(sigma2s)^2(sigma^**2s)^2(sigma2p_z)^2(pi2p_x^2=pi2p_y^2)(pi^**2p_x^1=pi^**2p_y^0)`
`bo=(10-5)/(2)=2.5`
`C_2^(2-):KK(sigma2s)^2(sigma^**2s)^2(pi2p_x^2=pi2p_y^2)(sigma2p_z)^2`
`bo=(10-4)/(2)=3.0`
Thus, the correct order of increasing bond order is
`He_2^(+) lt O_2^(-) lt NO lt C_2^(2-)`