Which of the following statements is are true about osmotic pressure?
I. Flow of solvent from solution across the semipermeable membrane can be stopped if extra pressure is applied on solution.
II. It is pressure that allow stops the flow of solvent.
III. It is pressure that allow flow of solvent across the semipermeable membrane.

Options

A. I, II
B. II, III
C. I, III
D. All of these

Answer

To determine which statements about osmotic pressure are true, let's analyze each statement step by step.

### Step 1: Understanding Osmotic Pressure
Osmotic pressure (π) is the pressure required to stop the flow of solvent molecules through a semipermeable membrane from a dilute solution to a more concentrated solution. This is a fundamental concept in the study of solutions and osmosis.

### Step 2: Analyzing Statement I
**Statement I:** "Flow of solvent from solution across the semipermeable membrane can be stopped if extra pressure is applied on solution."
- This statement is true. When extra pressure is applied to the solution side, it counteracts the osmotic pressure, stopping the flow of solvent from the solvent side to the solution side.

### Step 3: Analyzing Statement II
**Statement II:** "It is pressure that allows stops the flow of solvent."
- This statement is also true. The osmotic pressure is indeed the pressure that stops the flow of solvent across the semipermeable membrane.

### Step 4: Analyzing Statement III
**Statement III:** "It is pressure that allows flow of solvent across the semipermeable membrane."
- This statement is false. Osmotic pressure does not allow the flow of solvent; rather, it is the pressure that opposes the flow of solvent. The natural flow of solvent occurs from a region of lower solute concentration to a region of higher solute concentration until equilibrium is reached, but osmotic pressure is what stops that flow when applied.

### Conclusion
Based on the analysis:
- Statement I is true.
- Statement II is true.
- Statement III is false.

Thus, the true statements about osmotic pressure are I and II.

### Final Answer
The true statements about osmotic pressure are:
- I and II.

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