Question

Evaluate the correctness of the given statements.
I. Negative deviation occurs when A-B interactions are stronger than A-A and B-B. 
II. Reverse osmosis requires applied pressure greater than osmotic pressure. 

• A. Both Statement-I and Statement-II are correct
• B. Both Statement-I and Statement-II are incorrect
• C. Statement-I is correct but Statement-II is not correct
• D. Statement-I is not correct but Statement-II is correct

Hint:

Negative deviation in solutions means stronger A-B interactions, leading to lower vapour pressure than expected.

Answer 1

The Correct Option is D

Step 1: Evaluating Statement-I
- Negative deviation occurs when A-B interactions are stronger than A-A and B-B.
- Given statement is incorrect because it states A-B is weaker.
Step 2: Evaluating Statement-II
- Reverse osmosis requires applied pressure greater than osmotic pressure.
- This statement is correct. \bigskip

Answer 2

Step 1: Evaluating Statement-I (About Negative Deviation from Raoult’s Law)
- In an ideal solution, the interactions between unlike molecules (A-B) are equal to those between like molecules (A-A and B-B), so the solution obeys Raoult’s law exactly.
- Negative deviation occurs when the A-B interactions are stronger than both A-A and B-B interactions. This stronger attraction causes molecules to hold together more tightly, lowering the vapor pressure below the ideal prediction.
- The given statement incorrectly claims that negative deviation happens because A-B interactions are weaker, which is false. Weaker A-B interactions actually cause positive deviation, where vapor pressure is higher than ideal.
- Therefore, Statement-I is incorrect.

Step 2: Evaluating Statement-II (About Reverse Osmosis)
- Reverse osmosis is the process where solvent molecules move through a semipermeable membrane from a concentrated solution to a dilute solution, opposite to natural osmosis.
- To achieve this, an external pressure greater than the osmotic pressure must be applied to the concentrated side, forcing solvent molecules against their concentration gradient.
- The statement correctly notes the necessity of applied pressure exceeding osmotic pressure, so Statement-II is correct.

Summary:
- Statement-I is false because negative deviation requires stronger A-B interactions, not weaker.
- Statement-II is true because reverse osmosis demands applied pressure greater than osmotic pressure.

Additional Notes:
- Positive deviation arises when A-B interactions are weaker, leading to higher vapor pressure than ideal.
- Reverse osmosis is extensively used in water purification and desalination processes.