Which of the following species does not exist under normal condition ?

Options

A. `Be_2^+`
B. `Be_2`
C. `B_2`
D. `Li_2`

Answer

B

Explanation

Key Idea Molecules with zero bond order , do not exist.
According to molecular orbital theory,
(a)`Be_2^+`(4+4-1=7)
`=sigma1s^2 , overset***1s^2,sigma2s^2 , overset***2s^1`
Bond order (BO) `=(4-3)/2=0.5`
(b)`Be_2^+`(4+4=8)
`=sigma1s^2 , overset***1s^2,sigma2s^2 , overset***2s^2`
Bond order (BO) `=(4-4)/2=0`
(c )`B_2^+`(5+5=10)
`=sigma1s^2 , overset***1s^2,sigma2s^2 , overset***2s^1,pi2p_x^1~~pi2p_y^1`
Bond order (BO) `=(6-4)/2=1`
(d)`Li_2^+`(3+3=6)
`=sigma1s^2 , overset***1s^2,sigma2s^2`
Bond order (BO) `=(4-2)/2=1`
Thus, `Be_2` does not exist under normal conditions.