Which of the following are true?

Options

A. van der waals forces are reponsible for the formation of molecular crytals
B. Branching lower the boiling points of isomeric organic due to decrease in van der waals forces
C. In graphite, van der waal forces act between the carbon layers
D. In diamond, van der waal forces act between the carbon layers

Answer

To determine which statements are true regarding Van der Waals forces and their implications in molecular structures, we will analyze each statement step by step.

### Step-by-Step Solution:

1. **Understanding Van der Waals Forces**:
- Van der Waals forces are weak intermolecular forces that arise from temporary dipoles created when electron distributions in molecules become uneven. These forces play a significant role in the physical properties of substances, especially in molecular crystals.

**Hint**: Recall that Van der Waals forces include dipole-dipole interactions, dipole-induced dipole interactions, and London dispersion forces.

2. **Statement 1: Van der Waals forces are responsible for the formation of the molecular crystal**:
- This statement is **true**. Van der Waals forces facilitate the attraction between molecules, leading to the formation of molecular crystals.

**Hint**: Consider how molecular crystals are structured and the types of forces that hold them together.

3. **Statement 2: Branching lowers the boiling point of isomeric organic compounds due to a decrease in Van der Waals forces**:
- This statement is also **true**. In branched isomers, the surface area available for intermolecular interactions decreases, leading to weaker Van der Waals forces and consequently lower boiling points.

**Hint**: Think about how molecular shape affects surface area and intermolecular interactions.

4. **Statement 3: In graphite, Van der Waals forces act between the carbon layers**:
- This statement is **true**. In graphite, the layers of carbon atoms are held together by Van der Waals forces, allowing them to slide over one another, which is why graphite is slippery.

**Hint**: Visualize the layered structure of graphite and how layers interact with each other.

5. **Statement 4: In diamond, Van der Waals forces act between the carbon layers**:
- This statement is **false**. Diamond has a three-dimensional tetrahedral structure where each carbon atom forms four strong covalent bonds with neighboring carbon atoms. There are no layers in diamond, and thus no Van der Waals forces acting between layers.

**Hint**: Compare the structures of diamond and graphite to understand the differences in bonding.

### Conclusion:
- **True Statements**: 1, 2, and 3
- **False Statement**: 4

### Summary:
- Van der Waals forces are crucial for molecular crystal formation.
- Branching in organic compounds reduces boiling points due to decreased surface area.
- In graphite, Van der Waals forces act between layers, while in diamond, covalent bonds dominate.