The absolute zero is the temperature at which

Options

A. water freezes
B. all substances exist in solid
C. molecular motion ceases
D. all of these

Answer

**Step-by-Step Solution:**

1. **Understanding Absolute Zero:**
- Absolute zero is defined as the lowest possible temperature where all molecular motion ceases. This means that at absolute zero, the kinetic energy of the molecules is minimal, and they are in their lowest energy state.

2. **Temperature Scale:**
- Absolute zero is measured in Kelvin (K). The value of absolute zero is 0 K. In Celsius, this temperature is equivalent to -273.15 °C.

3. **Behavior of Substances at Absolute Zero:**
- At absolute zero, all substances theoretically exist in a solid state. This is because, at this temperature, the thermal energy is so low that the molecules cannot overcome the forces holding them in a solid structure.

4. **Freezing of Water:**
- Water, which normally freezes at 0 °C, will certainly freeze at absolute zero since it is a much lower temperature. Therefore, at absolute zero, water will be in a solid state (ice).

5. **Conclusion:**
- Thus, the absolute zero is the temperature at which:
- All molecular motion ceases.
- All substances exist in solid form.
- Water freezes.

**Final Answer:**
The absolute zero is the temperature at which all molecular motion ceases, all substances exist in solid form, and water freezes.

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