When a solution is separated from a solvent by a semi-permeable membrane, then the phenomenon taking place is called as

Options

A. Osmosis
B. Diffusion
C. Solubility
D. None

Explanation

To solve the question, we need to understand the concept of a semi-permeable membrane and the process that occurs when a solution is separated from a solvent by such a membrane.

### Step-by-Step Solution:

1. **Understanding Semi-Permeable Membrane**:
A semi-permeable membrane is a barrier that allows certain molecules or ions to pass through it while blocking others. In the context of solutions and solvents, it typically allows the solvent molecules to pass but not the solute particles.

**Hint**: Remember that a semi-permeable membrane selectively allows the passage of certain substances.

2. **Identifying the Components**:
- On one side of the membrane, we have a **solution** (which contains both solute and solvent).
- On the other side, we have a **pure solvent** (which contains only solvent molecules).

**Hint**: Visualize the setup: one side has solute and solvent, while the other side has only solvent.

3. **Concentration Gradient**:
The concentration of solvent molecules is higher on the side of the pure solvent compared to the side of the solution. This creates a concentration gradient.

**Hint**: Concentration gradients drive the movement of molecules from areas of high concentration to areas of low concentration.

4. **Movement of Solvent Molecules**:
Due to the concentration gradient, solvent molecules will move from the area of higher concentration (pure solvent side) to the area of lower concentration (solution side). This movement continues until equilibrium is reached.

**Hint**: Think about how water moves to balance concentrations on both sides of the membrane.

5. **Defining the Phenomenon**:
The process described above, where solvent molecules move from the pure solvent to the solution through a semi-permeable membrane, is known as **osmosis**.

**Hint**: Osmosis specifically refers to the movement of solvent molecules, typically water, across a semi-permeable membrane.

### Final Answer:
The phenomenon taking place when a solution is separated from a solvent by a semi-permeable membrane is called **osmosis**.