Question

Which one of the following pairs is an example of polar molecular solids ?

• A. HCl (s), AlN (s)
• B. MgO (s), SO₂(s)
• C. SO₂(s), NH₃(s)
• D. SO₂(s), CO₂(s)

Answer 1

The Correct Option is C

To solve this question, we need to understand the concept of polar molecular solids. Polar molecular solids are composed of molecules that have a permanent dipole moment. This means that the molecule has a non-uniform distribution of electrons, leading to partial positive and negative charges.

Let's evaluate the given options:

1. HCl (s), AlN (s): HCl is a polar molecule due to the electronegativity difference between hydrogen and chlorine, whereas AlN is not a molecular solid but an ionic solid. Therefore, this pair cannot be classified as polar molecular solids.

2. MgO (s), SO₂ (s): MgO is an ionic compound and not a molecular solid. SO₂ is a polar molecular solid due to its bent shape which causes a net dipole moment, but since MgO is not a polar molecular solid, this pair is not correct.

3. SO₂ (s), NH₃ (s): Both SO₂ and NH₃ are polar molecular solids. SO₂ has a bent shape contributing to its polarity, while NH₃ has a trigonal pyramidal shape with a net dipole moment due to the difference in electronegativity between nitrogen and hydrogen. This makes this pair a correct example of polar molecular solids.

4. SO₂ (s), CO₂ (s): While SO₂ is a polar molecular solid, CO₂ is a nonpolar molecular solid due to its linear geometry which results in the cancellation of dipole moments. Therefore, this pair is incorrect.

The correct answer is SO₂ (s), NH₃ (s) as both are polar molecular solids due to their molecular geometries and resulting dipole moments.