Define reverse osmosis. Give one use of it.

Explanation

### Step-by-Step Text Solution:

**Step 1: Define Osmosis**
- Osmosis is the process in which solvent molecules move from a region of lower solute concentration to a region of higher solute concentration through a semi-permeable membrane. This movement continues until equilibrium is reached.

**Step 2: Explain Semi-Permeable Membrane**
- A semi-permeable membrane is a barrier that allows certain molecules or ions to pass through while blocking others. In osmosis, it permits the passage of solvent molecules but not solute particles.

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