Molecular weight of macromolecules are determined by:

Options

A. Elevation of boiling point
B. Depression in freezing point
C. Osmotic pressure
D. None of these

Answer

To determine the molecular weight of macromolecules, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Macromolecules**:
- Macromolecules are large molecules composed of thousands of atoms. Examples include proteins, nucleic acids, and synthetic polymers.

2. **Concept of Molecular Weight**:
- The molecular weight (or molar mass) of a substance is the mass of one mole of that substance, usually expressed in grams per mole (g/mol).

3. **Methods to Determine Molecular Weight**:
- There are various methods to determine the molecular weight of macromolecules, including colligative properties such as boiling point elevation, freezing point depression, and osmotic pressure.

4. **Focus on Osmotic Pressure**:
- Among the methods mentioned, osmotic pressure is particularly useful for macromolecules. Osmotic pressure is the pressure required to stop the flow of solvent into a solution through a semipermeable membrane.

5. **Relation Between Osmotic Pressure and Molecular Weight**:
- The osmotic pressure (π) of a solution is directly proportional to the number of solute particles in a given volume of solution. The formula for osmotic pressure is given by:
\[ \pi = \frac{n}{V}RT \]
where \( n \) is the number of moles of solute, \( V \) is the volume of the solution, \( R \) is the gas constant, and \( T \) is the temperature in Kelvin.

6. **Calculating Molecular Weight**:
- From the osmotic pressure, we can determine the number of moles of the solute. If we know the weight of the solute used to prepare the solution, we can calculate the molecular weight using the formula:
\[ \text{Molecular Weight} = \frac{\text{Weight of solute (g)}}{n} \]
- Here, \( n \) can be derived from the osmotic pressure equation.

7. **Conclusion**:
- Therefore, the molecular weight of macromolecules can be accurately determined using osmotic pressure, making option 3 the correct answer.

### Final Answer:
The molecular weight of macromolecules is determined by osmotic pressure (Option 3).

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