By convention the water potential of pure water at standard temperatures, which is not under any pressure, is taken to be

Options

A. 100 atm
B. Zero
C. More than 0 atm
D. Less than 0 atm

Answer

To solve the question regarding the water potential of pure water at standard temperatures, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Water Potential**: Water potential (Ψ) is a measure of the potential energy in water and its ability to perform work. It is influenced by solute concentration and pressure.

2. **Pure Water Definition**: Pure water is defined as water that does not contain any solutes. This means it has the highest possible water potential because there are no solutes to lower it.

3. **Water Potential of Pure Water**: By convention, the water potential of pure water at standard temperature and pressure (STP) is defined to be zero. This is because it is the reference point against which other solutions are measured.

4. **Comparison with Other Solutions**: When solutes are added to water, the water potential decreases (becomes negative) because the presence of solutes reduces the number of free water molecules, thus reducing the potential energy.

5. **Conclusion**: Therefore, the water potential of pure water at standard temperatures and pressure, which is not under any pressure, is taken to be **zero**.

### Final Answer:
The water potential of pure water at standard temperatures, which is not under any pressure, is taken to be **zero**.

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