If the external solution balances the osmotic pressure of cytoplasm. It is said to be -

Options

A. hypotonic
B. Hypertonic
C. Atonic
D. Isotonic

Answer

To solve the question, "If the external solution balances the osmotic pressure of cytoplasm, it is said to be -", we can follow these steps:

### Step-by-Step Solution:

1. **Understand Osmotic Pressure**: Osmotic pressure is the pressure required to prevent the flow of water across a semipermeable membrane due to solute concentration. The more solute present, the higher the osmotic pressure.

2. **Identify the Context**: The question refers to a plant cell placed in an external solution. The osmotic pressure of the cytoplasm of the plant cell is influenced by the concentration of solutes within it.

3. **Compare Solute Concentrations**: If the external solution has the same solute concentration as the cytoplasm of the plant cell, it means that the osmotic pressures are equal.

4. **Define the Conditions**:
- **Hypotonic Solution**: A solution with a lower solute concentration compared to the cytoplasm, leading to water entering the cell.
- **Hypertonic Solution**: A solution with a higher solute concentration compared to the cytoplasm, causing water to leave the cell.
- **Isotonic Solution**: A solution with the same solute concentration as the cytoplasm, resulting in no net movement of water.

5. **Conclusion**: Since the question states that the external solution balances the osmotic pressure of the cytoplasm, it indicates that the concentrations are equal. Therefore, the correct term to describe this condition is "isotonic".

### Final Answer:
The external solution that balances the osmotic pressure of the cytoplasm is said to be **isotonic**.

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