Which of the following statements is not correct about molecular crystals ?

Options

A. They are generally soft and easily compressible
B. They are good conductors of electricity as the electrons are delocalised in the bonds
C. They have low melting and boiling points
D. They consist of polar or non-polar molecules .

Explanation

To determine which statement is not correct about molecular crystals, let's analyze each option step by step:

### Step 1: Analyze the first statement
**Statement A:** "They are generally soft and easily compressible."
- Molecular crystals are typically composed of molecules held together by weak intermolecular forces (like Van der Waals forces). This results in a structure that is generally soft and can be easily compressed.
**Conclusion:** This statement is correct.

### Step 2: Analyze the second statement
**Statement B:** "They are good conductors of electricity as electrons are delocalized in the bonds."
- In molecular crystals, the bonding involves covalent bonds between atoms within the molecules, but these bonds do not allow for free movement of electrons. The electrons are not delocalized in the same way as in metallic or some covalent network solids. Therefore, molecular crystals do not conduct electricity well and are generally considered insulators.
**Conclusion:** This statement is not correct.

### Step 3: Analyze the third statement
**Statement C:** "They have low melting and boiling points."
- Molecular crystals usually have low melting and boiling points compared to ionic or metallic crystals due to the weak intermolecular forces holding them together.
**Conclusion:** This statement is correct.

### Step 4: Analyze the fourth statement
**Statement D:** "They consist of polar and nonpolar molecules."
- Molecular crystals can indeed consist of both polar and nonpolar molecules, depending on the nature of the substances involved.
**Conclusion:** This statement is correct.

### Final Conclusion
The statement that is not correct about molecular crystals is **Statement B**: "They are good conductors of electricity as electrons are delocalized in the bonds."

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