Compreshension -I
The experimental values of colligative properties of many solutes in solution resembles calculated value of colligative properties.
However in same cases, the experimental value of colligative property differ widely than those obtained by calculation. Such experimental values of colligative properties are known as Abnormal values of colligative properties are :
(i) Dissociation of solute : It increases the colligative properties.
(ii) Association of solute : It decreases the colligative properties
e.g. : Dimerisation of acetic acid in benzene
If degree of dissociation of an electrolyte `A_(2)B_(3)` is 25% in a solvent, then

Options

A. Normal boiling point =Experimental boiling point
B. Normal freezing point `gt` Experimental freezing point
C. Normal osmotic pressure`=(1)/(2)` Experimental osmotic pressure
D. Normal molecular weight `=(1)/(4)` Experimental molecular weight

Answer

To solve the problem regarding the degree of dissociation of the electrolyte \( A_2B_3 \) and its effect on colligative properties, we will follow these steps:

### Step 1: Understand the Degree of Dissociation
The degree of dissociation (\( \alpha \)) is given as 25%, which can be expressed as:
\[ \alpha = \frac{25}{100} = 0.25 \]

### Step 2: Determine the Number of Particles Produced
The electrolyte \( A_2B_3 \) dissociates according to the following reaction:
\[ A_2B_3 \rightarrow 2A + 3B \]
From this reaction, we can see that one formula unit of \( A_2B_3 \) produces a total of \( 2 + 3 = 5 \) particles when fully dissociated.

### Step 3: Calculate the Van 't Hoff Factor (i)
The Van 't Hoff factor (\( i \)) can be calculated using the formula:
\[ i = 1 + (n - 1) \alpha \]
where \( n \) is the total number of particles produced from one formula unit of the solute. Here, \( n = 5 \) and \( \alpha = 0.25 \):
\[ i = 1 + (5 - 1) \times 0.25 = 1 + 4 \times 0.25 = 1 + 1 = 2 \]

### Step 4: Analyze the Effect on Colligative Properties
1. **Normal Boiling Point**: The normal boiling point is equal to the experimental boiling point.
2. **Normal Freezing Point**: The normal freezing point is greater than the experimental freezing point. Since \( i > 1 \), the freezing point depression will be greater, indicating that the freezing point of the solution decreases.
3. **Normal Osmotic Pressure**: The normal osmotic pressure is equal to half of the experimental osmotic pressure.
4. **Normal Molecular Weight**: The normal molecular weight is equal to one-fourth of the experimental molecular weight.

### Conclusion
From the above analysis, we can conclude:
- The dissociation of the electrolyte \( A_2B_3 \) leads to an increase in colligative properties.
- The calculated values differ from the experimental values due to the degree of dissociation.