Every pure substance has one specific temperature-pressure combination where its solid, liquid, and vapor phases coexist at equilibrium. For water, this point sits close to 0°C but is quoted precisely as 0.0098°C, at a low pressure of 4.58 mmHg. This constant comes up often in physical pharmacy when discussing phase diagrams and supercritical behavior.
- 0.098°C and 4.58 mmHg: The pressure figure is fine, but shifting the decimal point on the temperature turns 0.0098 into 0.098, a tenfold error. That rules this option out.
- 0.0098°F and 4.58 mmHg: Reusing the correct digits but swapping the unit to Fahrenheit changes what the number actually represents. 0.0098°C is roughly 32°F, so labeling the same digits as Fahrenheit describes a completely different, incorrect temperature.
- 0.098°F and 4.58 mmHg: Wrong on both counts, the digit placement and the temperature unit, so this cannot be right either.
- 0.0098°C and 4.58 mmHg: This is the figure recorded for water's triple point: 0.0098°C and 4.58 mmHg (about 611.7 Pa), the standard fixed point behind the Kelvin scale's original definition.
Matching both the number and the unit correctly points to one option only.
So the correct answer is 0.0098°C and 4.58 mmHg.