Freezing point of a solution is smaller than freezing point of a solvent. It is due to :

Options

A. `/_\H` of solution and solvent is almost identical since intermolecular force between solvent molecules are involved
B. `/_\S` solution (between solution and solid ) is lager than that of the `/_\S`of solvent (between solvent and solid)
C. `/_\S` of then solution is smaller than that of the solvent
D. `/_\H` of the solution is much higher than of solvent but `/_\S` of solvent than that of the solvent

Answer

To solve the question regarding why the freezing point of a solution is lower than that of the solvent, we can break it down into a few key steps:

### Step 1: Understand Freezing Point Depression
The phenomenon where the freezing point of a solution is lower than that of the pure solvent is known as freezing point depression. This occurs when a solute is added to a solvent.

**Hint:** Remember that adding a solute to a solvent disrupts the orderly arrangement of solvent molecules, affecting their freezing point.

### Step 2: Identify Interactions in the Solution
In a pure solvent, the interactions are primarily solvent-solvent interactions. However, when a solute is added, the interactions in the solution consist of solute-solvent, solute-solute, and solvent-solvent interactions.

**Hint:** Think about how the presence of solute particles changes the way solvent molecules interact with each other.

### Step 3: Consider the Role of Solute Particles
The addition of solute particles acts as impurities in the solvent. These impurities disrupt the normal freezing process of the solvent, requiring a lower temperature to achieve the same solid-state structure.

**Hint:** Consider how impurities generally affect the properties of a pure substance.

### Step 4: Analyze Entropy Changes
The entropy (ΔS) of a solution is greater than that of the pure solvent because there are more particles in the solution. Increased entropy means that the system is more disordered, which contributes to the lowering of the freezing point.

**Hint:** Recall that higher entropy typically corresponds to a lower tendency to form a solid.

### Step 5: Relate ΔH and ΔS
The relationship between enthalpy change (ΔH) and entropy change (ΔS) can be expressed in terms of the freezing point. For a solution, the ratio ΔH/ΔS decreases, while for the solvent, it increases. This change in ratio leads to a decrease in the freezing point of the solution.

**Hint:** Think about how changes in energy and disorder influence the phase transitions of substances.

### Conclusion
The freezing point of a solution is lower than that of the solvent primarily due to the presence of solute particles that disrupt the solvent's structure and increase the entropy of the system. This results in a lower freezing point for the solution compared to the pure solvent.

**Final Answer:** The freezing point of a solution is smaller than the freezing point of a solvent due to the presence of solute particles that increase the entropy of the solution, leading to freezing point depression.