Question

The molecule (ion) having one unpaired electron is

• A. NO
• B. CO
• C. CN\(^-\)
• D. O\(_2\)

Hint:

NO is a well-known paramagnetic molecule with one unpaired electron. O\(_2\) has two unpaired electrons and is also paramagnetic.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The number of unpaired electrons can be determined from the molecular orbital (MO) electronic configuration.
Step 2: Detailed Explanation:
\begin{itemize} \item (A) NO: 15 electrons. MO configuration: \(KK (\sigma_{2s})^2 (\sigma_{2s}^*)^2 (\pi_{2px})^2 (\pi_{2py})^2 (\sigma_{2pz})^2 (\pi_{2px}^*)^1\). One unpaired electron. \item (B) CO: 14 electrons. MO configuration: \(KK (\sigma_{2s})^2 (\sigma_{2s}^*)^2 (\pi_{2px})^2 (\pi_{2py})^2 (\sigma_{2pz})^2\). No unpaired electrons. \item (C) CN\(^-\): 14 electrons (C has 6, N has 7, plus 1 extra = 14). Same as CO, no unpaired electrons. \item (D) O\(_2\): 16 electrons. MO configuration: \(KK (\sigma_{2s})^2 (\sigma_{2s}^*)^2 (\sigma_{2pz})^2 (\pi_{2px})^2 (\pi_{2py})^2 (\pi_{2px}^*)^1 (\pi_{2py}^*)^1\). Two unpaired electrons. \end{itemize}
Step 3: Final Answer:
NO has one unpaired electron, option (A).