Osmotic Pressure

The problem requires determining in which experiments pure water can be obtained in part-II of the vessel, given the osmotic pressure of seawater is 1.05 atm. To understand when pure water can be obtained, we need to apply the concept of osmotic pressure. Osmotic pressure ( ) is the pressure required to stop the flow of a solvent into a solution through a semipermeable membrane. The solvent naturally flows from lower to higher solute concentration (from lower to higher osmotic pressure) until equilibrium is reached.

For pure water to be obtained in part-II, the osmotic pressure of the solution in part-II must be less than in part-I, which implies water flows from part-I to part-II. Let's analyze each experiment:

1. **Experiment I:** The osmotic pressure is 1.05 atm in part-I (seawater), and 0 atm in part-II (pure water). Since the pressure is higher in part-I, water moves towards part-II, allowing pure water accumulation.

2. **Experiment II:** Here, part-I has 0 atm (distilled water) while part-II has seawater at 1.05 atm. Water will move from part-I to part-II, leading to no accumulation of pure water in part-II.

3. **Experiment III:** Similar to experiment I, part-I contains seawater with a pressure of 1.05 atm, and part-II contains distilled water with 0 atm. Water will flow from part-I to part-II, allowing pure water accumulation.

4. **Experiment IV:** Part-I has a salt solution at 2 atm while part-II has 0 atm. Though the pressure difference would facilitate water to part-II, the osmotic pressure in part-I exceeding that of seawater suggests it doesn't fit the specific case of seawater osmotic pressures matching only.

Based on these analyses, experiments I and III result in pure water accumulation in part-II since water moves from a higher to lower osmotic pressure. Thus, the correct choice is only.