An osmometer is filled with 0.5 M solution of NaCl in water. In which of the following solutions it must be immersed in order to make it shrink

Options

A. 0.05 M
B. 0.75 M
C. 0.5 M
D. Distilled water

Answer

To determine in which solution an osmometer filled with a 0.5 M NaCl solution must be immersed in order to make it shrink, we need to understand the concept of tonicity and osmotic pressure.

### Step-by-Step Solution:

1. **Understanding Osmosis**:
- Osmosis is the movement of water across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration.

2. **Identifying the Solution in the Osmometer**:
- The osmometer is filled with a 0.5 M NaCl solution. This means the concentration of solute (NaCl) in the osmometer is 0.5 M.

3. **Defining Tonicity**:
- Tonicity refers to the relative concentration of solutes in two solutions separated by a semipermeable membrane. There are three types of solutions:
- **Isotonic**: Same solute concentration as the solution in the osmometer (0.5 M NaCl).
- **Hypotonic**: Lower solute concentration than the solution in the osmometer (less than 0.5 M NaCl).
- **Hypertonic**: Higher solute concentration than the solution in the osmometer (greater than 0.5 M NaCl).

4. **Condition for Shrinking**:
- For the osmometer to shrink, it must be placed in a hypertonic solution. In this case, water will move out of the osmometer into the surrounding solution, causing it to shrink.

5. **Analyzing Given Options**:
- We need to find a solution with a concentration greater than 0.5 M NaCl.
- If the options are:
- A) 0.05 M NaCl (hypotonic)
- B) 0.75 M NaCl (hypertonic)
- C) 0.5 M NaCl (isotonic)
- D) Distilled water (hypotonic)
- The only option that is hypertonic (greater than 0.5 M) is **B) 0.75 M NaCl**.

6. **Conclusion**:
- Therefore, to make the osmometer shrink, it must be immersed in a **0.75 M NaCl solution**.