Question

Number of molecules/species from the following having one unpaired electron is ________.
\( \text{O}_2, \, \text{O}_2^{1-}, \, \text{NO}, \, \text{CN}^{1-}, \, \text{O}_2^{2-} \)

Answer 1

Correct Answer: 2

According to Molecular Orbital Theory (M.O.T.):

For \( O_2 \):

Number of unpaired electrons = 2

For \( O_2^{1-} \):

Number of unpaired electrons = 1

For NO:

Number of unpaired electrons = 1

For \( CN^- \):

Number of unpaired electrons = 0

For \( O_2^{2-} \):

Number of unpaired electrons = 0

Therefore, the number of species having exactly one unpaired electron is 2 (\( O_2^{1-} \) and NO).

Answer 2

Step 1: Molecules/species to analyze.
- \( \text{O}_2 \)
- \( \text{O}_2^{1-} \) (superoxide ion)
- \( \text{NO} \) (nitric oxide)
- \( \text{CN}^{1-} \) (cyanide ion)
- \( \text{O}_2^{2-} \) (peroxide ion)

Step 2: Electron configuration and unpaired electrons.
- \( \text{O}_2 \): Has two unpaired electrons due to its antibonding π* orbitals.
- \( \text{O}_2^{1-} \): Has one unpaired electron (one extra electron compared to \( \text{O}_2 \)).
- \( \text{NO} \): Has one unpaired electron in its molecular orbital.
- \( \text{CN}^{1-} \): All electrons paired; no unpaired electrons.
- \( \text{O}_2^{2-} \): All electrons paired; no unpaired electrons.

Step 3: Count of species with one unpaired electron.
Species with exactly one unpaired electron are:
- \( \text{O}_2^{1-} \)
- \( \text{NO} \)

Final Answer:
Number of species with one unpaired electron =
\[ \boxed{2} \]