Which of the following is closest to the melting point of ammonia (NH_3)?

• A. -77^ext{o}C
• B. -33^ext{o}C
• C. -78^ext{o}C
• D. 0^ext{o}C

Answer: (A)

Verified step by step guidance

1. Understand that the melting point of a substance is the temperature at which it changes from solid to liquid under standard pressure.
2. Recall or look up the known physical properties of ammonia (NH_3), specifically its melting point.
3. Compare the given options (-77°C, -33°C, -78°C, 0°C) to the known melting point of ammonia.
4. Note that ammonia has a melting point close to -78°C, which is a well-documented value in chemistry references.
5. Identify the option closest to this known value, which is -78°C, as the correct answer.