Question

In the following, the number of paramagnetic molecules are: O\(_2\), N\(_2\), F\(_2\), B\(_2\), Cl\(_2\).

• A. 1
• B. 2
• C. 3
• D. 4

Hint:

A molecule is paramagnetic if it contains at least one unpaired electron in its molecular orbitals.

Answer 1

The Correct Option is C

Paramagnetism arises due to the presence of unpaired electrons in a molecule. Let’s analyze each molecule's electronic configuration to determine the number of paramagnetic molecules: 

- O\(_2\) (Oxygen): Oxygen molecule has a total of 16 electrons. According to molecular orbital theory, the electronic configuration for O\(_2\) is: \[ (\sigma_{1s})^2 (\sigma_{1s}^*)^2 (\sigma_{2s})^2 (\sigma_{2s}^*)^2 (\sigma_{2p_z})^2 (\pi_{2p_x})^1 (\pi_{2p_y})^1 (\pi_{2p_x}^*)^0 (\pi_{2p_y}^*)^0 \] This shows that there are 2 unpaired electrons, making O\(_2\) paramagnetic.

 - N\(_2\) (Nitrogen): Nitrogen molecule has a total of 14 electrons. Its molecular orbital configuration is: \[ (\sigma_{1s})^2 (\sigma_{1s}^*)^2 (\sigma_{2s})^2 (\sigma_{2s}^*)^2 (\sigma_{2p_z})^2 (\pi_{2p_x})^2 (\pi_{2p_y})^2 \] All electrons are paired in N\(_2\), so it is diamagnetic.

 - F\(_2\) (Fluorine): Fluorine molecule has a total of 18 electrons. The electronic configuration is: \[ (\sigma_{1s})^2 (\sigma_{1s}^*)^2 (\sigma_{2s})^2 (\sigma_{2s}^*)^2 (\sigma_{2p_z})^2 (\pi_{2p_x})^2 (\pi_{2p_y})^2 (\pi_{2p_x}^*)^1 (\pi_{2p_y}^*)^1 \] This configuration shows 2 unpaired electrons, making F\(_2\) paramagnetic.

 - B\(_2\) (Boron): Boron molecule has a total of 10 electrons. Its electronic configuration is: \[ (\sigma_{1s})^2 (\sigma_{1s}^*)^2 (\sigma_{2s})^2 (\sigma_{2s}^*)^2 (\pi_{2p_x})^1 (\pi_{2p_y})^1 \] This configuration shows 2 unpaired electrons, making B\(_2\) paramagnetic.

 - Cl\(_2\) (Chlorine): Chlorine molecule has a total of 18 electrons. The electronic configuration is: \[ (\sigma_{1s})^2 (\sigma_{1s}^*)^2 (\sigma_{2s})^2 (\sigma_{2s}^*)^2 (\sigma_{2p_z})^2 (\pi_{2p_x})^2 (\pi_{2p_y})^2 (\pi_{2p_x}^*)^1 (\pi_{2p_y}^*)^1 \] This configuration shows 2 unpaired electrons, making Cl\(_2\) paramagnetic. Thus, the paramagnetic molecules are O\(_2\), F\(_2\), and B\(_2\). Therefore, the number of paramagnetic molecules is 3.