Question

In $O_2^{-}$, $O_{2}and{O}_2^{2-}$ molecular species, the total number of anti-bonding electrons respectively are:

• A. 7, 6, 8
• B. 1, 0, 2
• C. 6, 6, 6
• D. 8, 6, 8

Answer 1

The correct option is A

7, 6, 8

To know the number of anti-bonding electrons, lets draw the MO energy level diagrams of $O_2^{-}$, $O_2$ and $O_2^{2-}$

The following is the MOT diagram for Dioxygen $O_2$ molecule:
As you can see, we have omitted the $1s$ orbitals for convenience. The $1s$ portion will be similar to the MOT diagram for $O_2^{-}$ ion show above.

Now let us take a look at the MOT diagram for the peroxide ion $O_2^{2-}$

Now, we know that

Bonding electrons are represented by $\sigma$ and $\pi$.

Anti-bonding electrons are represented by $\sigma$* and $\pi$*.

Therefore, from the above diagrams, we can see that,

Number of anti-bonding electrons in:

$O_2^{-}$ $\Rightarrow$ 7

$O_2$ $\Rightarrow$ 6

$O_2^{2-}$ $\Rightarrow$ 8