Molecular Orbitals of Helium and Lithium

Q.

Which of the following cannot exist on the basis of MO theory?

1. ${H_2}^{+}$

2. ${H{e}_2}^{+}$

3. $H{e}_2$

4. $O_2$

Q. If one of the electrons in the $H{e}_2$ molecule is taken to the next excited state, then the bond order in $H{e}_2$:

1. increases by 1
2. decreases by 1
3. increases by 0.5
4. no change

Q. The correct electronic configuration for $H_2^{-}$ is:

1. $\sigma {1s}^2$
2. $\sigma \left({1s}^1\right){\sigma }^{\ast }({1s}^1$)
3. $\sigma \left({1s}^2\right){\sigma }^{\ast }\left(1s^1\right)$
4. $\sigma {1s}^3$

Q. The correct electronic configuration for $H_2^{-}$ is:

1. $\sigma {1s}^2$
2. $\sigma \left({1s}^1\right){\sigma }^{\ast }({1s}^1$)
3. $\sigma \left({1s}^2\right){\sigma }^{\ast }\left(1s^1\right)$
4. $\sigma {1s}^3$

Q. According to molecular orbital theory, which of the following is true with respect to ${{\mathrm{Li}}_2}^{+}\mathrm{and}{{\mathrm{Li}}_2}^{-}$ ?

1. Both are unstable
2. ${\mathrm{Li}}_2^{+}$ is unstable and
   ${\mathrm{Li}}_2^{-}$ is stable
3. ${\mathrm{Li}}_2^{+}$ is stable and
   ${\mathrm{Li}}_2^{-}$ is unstable
4. Both are stable