Question

Observe the following list of molecules. Number of polar and non polar molecules are respectively
\(\text{NH}_3, \text{BF}_3, \text{NF}_3, \text{H}_2\text{S}, \text{CO}_2, \text{CH}_4, \text{CHCl}_3, \text{H}_2\text{O}\)

• A. 4, 4
• B. 3, 5
• C. 5, 3
• D. 2, 6

Hint:

Symmetrical molecules with identical surrounding atoms and no lone pairs on the central atom (e.g., \(\text{BF}_3, \text{CH}_4, \text{CO}_2\)) are usually non-polar. Asymmetry or lone pairs usually lead to polarity.

Answer 1

The Correct Option is C

Step 1: Determine Polarity of each molecule Polar molecules have a net dipole moment (\(\mu \neq 0\)). Non-polar molecules have zero net dipole moment (\(\mu = 0\)). 1. \(\text{NH}_3\): Pyramidal structure, unsymmetrical. Polar. 2. \(\text{BF}_3\): Trigonal planar, symmetrical. Dipoles cancel. Non-polar. 3. \(\text{NF}_3\): Pyramidal structure, unsymmetrical. Polar. 4. \(\text{H}_2\text{S}\): Bent structure, lone pairs on S. Polar. 5. \(\text{CO}_2\): Linear structure (\(\text{O=C=O}\)). Symmetrical. Non-polar. 6. \(\text{CH}_4\): Tetrahedral structure. Symmetrical. Non-polar. 7. \(\text{CHCl}_3\): Tetrahedral but atoms are different (3 Cl, 1 H). Unsymmetrical. Polar. 8. \(\text{H}_2\text{O}\): Bent structure, lone pairs on O. Polar.
Step 2: Count Polar molecules:
\(\text{NH}_3, \text{NF}_3, \text{H}_2\text{S}, \text{CHCl}_3, \text{H}_2\text{O}\). Total = 5. Non-polar molecules:
\(\text{BF}_3, \text{CO}_2, \text{CH}_4\). Total = 3. Final Answer:
5, 3.