Two aqueous solutions, A and B, are separated by a semi- permeable membrane. The osmotic pressure of solution A immediately begins to decrease. Which of the following statement is true ?

Options

A. (a) The solvent molecular are moving from the solution of higher osmotic pressure to that of lower osmotic pressure
B. (b) The initial osmotic pressure of solution B is greater than that of solution A.
C. (c) Solvent molecules are moving from solution B into solution A.
D. (d) Both (a) and (b) are true statements.

Answer

To solve the question regarding the two aqueous solutions A and B separated by a semi-permeable membrane, we need to analyze the situation based on the information provided about osmotic pressure.

### Step-by-Step Solution:

1. **Understanding Osmotic Pressure**:
- Osmotic pressure (π) is the pressure required to stop the flow of solvent into a solution through a semi-permeable membrane. It is directly related to the concentration of solute particles in the solution.

2. **Initial Conditions**:
- We have two solutions, A and B, separated by a semi-permeable membrane. Let’s denote the osmotic pressure of solution A as π1 and that of solution B as π2.

3. **Observation**:
- The problem states that the osmotic pressure of solution A (π1) immediately begins to decrease. This indicates that there is a change happening in the system.

4. **Analyzing the Change**:
- If π1 is decreasing, it suggests that the concentration of solute particles in solution A is decreasing. This can happen if solvent molecules are moving into solution A from solution B.

5. **Direction of Solvent Movement**:
- Solvent molecules move from an area of lower osmotic pressure to an area of higher osmotic pressure. Therefore, if π1 is decreasing, it implies that initially π1 must have been greater than π2 (i.e., π1 > π2).

6. **Conclusion**:
- Since solvent molecules are moving from solution B (lower osmotic pressure) to solution A (higher osmotic pressure), the correct statement is that solvent molecules are moving from solution B to solution A.

### Answer:
The correct statement is: **Solvent molecules are moving from solution B to solution A.**

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