Which of the following are true?

Options

A. Van der Waals forces are responsible for the formation of molecular crystals
B. Branching lowers the boiling points of isomeric organic compounds due to decrease in vander Waals forces of attraction
C. In graphite, van der Waals forces act between the carbon layers
D. In diamond, van der Waals forces act between the carbon layers

Answer

To determine which of the statements regarding chemical bonding and molecular interactions are true, we will analyze each statement step by step.

### Step 1: Analyze the First Statement
**Statement:** Van der Waals forces are responsible for the formation of molecular crystals.

**Explanation:**
- Molecular crystals, such as iodine (I2), are held together by weak intermolecular forces known as Van der Waals forces.
- Iodine molecules (I2) are large and have significant dispersion forces due to their size.
- These dispersion forces allow the I2 molecules to attract each other, leading to the formation of solid molecular crystals.

**Conclusion:** This statement is **true**.

### Step 2: Analyze the Second Statement
**Statement:** If we do branching, the boiling point of organic compounds decreases due to Van der Waals forces.

**Explanation:**
- In linear organic compounds, molecules can pack closely together, leading to stronger Van der Waals interactions.
- When branching occurs, the shape of the molecule becomes more compact, reducing the surface area available for intermolecular interactions.
- As a result, the weaker interactions lead to a lower boiling point compared to their linear counterparts.

**Conclusion:** This statement is **true**.

### Step 3: Analyze the Third Statement
**Statement:** In graphite, the Van der Waals forces act between carbon-carbon layers.

**Explanation:**
- Graphite consists of layers of carbon atoms bonded covalently in a plane, with weak Van der Waals forces acting between these layers.
- The layers can slide over one another due to these weak forces, which is why graphite is lubricative and can be used in pencils.

**Conclusion:** This statement is **true**.

### Step 4: Analyze the Fourth Statement
**Statement:** In diamond, Van der Waals forces act between the carbon layers.

**Explanation:**
- Diamond has a tetrahedral structure where each carbon atom is covalently bonded to four other carbon atoms.
- This structure is very tightly packed, leaving no space for Van der Waals forces to act between the carbon atoms.
- All interactions in diamond are strong covalent bonds, not Van der Waals forces.

**Conclusion:** This statement is **false**.

### Final Conclusion
- **True Statements:** 1, 2, and 3 are true.
- **False Statement:** 4 is false.