On the Fahrenheit temperature scale, at what temperature does pure water freeze at standard atmospheric pressure?

Introduction / Context:
Different temperature scales use different reference points. In everyday life in some countries, the Fahrenheit scale is used instead of the Celsius scale. Knowing key fixed points such as the freezing and boiling temperatures of water on different scales is important in physics, meteorology and daily life. This question asks you to recall the freezing point of pure water on the Fahrenheit scale at normal atmospheric pressure.

Given Data / Assumptions:
- The substance is pure water.
- The process is freezing, meaning change from liquid to solid.
- Standard atmospheric pressure is assumed (approximately 1 atm).
- The options are 0, 17, 32 and 39 on the Fahrenheit scale.

Concept / Approach:
On the Celsius scale, pure water freezes at 0 C and boils at 100 C under standard pressure. On the Fahrenheit scale, the same physical freezing point corresponds to 32 F, and the boiling point corresponds to 212 F. The conversion between the two scales is given by F = (9/5) * C + 32. Substituting C = 0 gives F = 32. Therefore, the correct freezing temperature in Fahrenheit is 32.

Step-by-Step Solution:
Step 1: Recall that the freezing point of water in Celsius is 0 C. Step 2: Use the conversion formula F = (9/5) * C + 32. Step 3: Substitute C = 0 into the formula: F = (9/5) * 0 + 32. Step 4: This simplifies to F = 32. Step 5: Match 32 with the given options and choose it as the correct answer.

Verification / Alternative check:
Everyday references confirm this result. In countries using the Fahrenheit scale, weather reports mention that water will freeze when the temperature falls to around 32 F. Road signs warning of ice often highlight this number. Also, using the same formula for the boiling point, with C = 100, we get F = (9/5) * 100 + 32 = 212, which matches the known boiling point in Fahrenheit, confirming that the conversion and the 32 F freezing point are consistent.

Why Other Options Are Wrong:
0: Zero on the Fahrenheit scale corresponds to about minus 17.8 C, much colder than the freezing point of water.
17: Seventeen Fahrenheit is still below the freezing point of water and does not correspond to a key fixed point on the scale.
39: Thirty nine Fahrenheit is above the freezing point of water and would represent cold but still liquid conditions for water.

Common Pitfalls:
Students sometimes mix up Celsius and Fahrenheit values, assuming that 0 on any scale means freezing or that 100 always means boiling. It is important to remember that the Fahrenheit scale is shifted and stretched differently. Always recall at least the two key benchmarks: 32 F for freezing and 212 F for boiling of water at standard pressure. These help you quickly answer such questions and also estimate conversions between the two scales.

Final Answer:
On the Fahrenheit scale, pure water freezes at 32 degrees Fahrenheit.