Question

select the correct answer.
lars observes a substance to be a solid and to float in water at room temperature (23°c). based on the given properties, which substance is the most likely identity of this sample?

substance	melting point (°c)	boiling point (°c)	density at room temperature (g/cm³)
cetyl alcohol	49.3	344	0.811
dichlorobenzene	53.5	174	1.25
sulfur hexafluoride	-64	-50.8	0.00617

a. carbon tetrachloride
b. cetyl alcohol
c. dichlorobenzene
d. sulfur hexafluoride

Explanation:

Step1: Analyze state at 23°C

For a substance to be solid at 23°C, its melting point must be ≤ 23°C? No, wait: melting point is the temp where solid turns to liquid. So if a substance is solid at 23°C, its melting point must be > 23°C (because if melting point ≤23, it would be liquid or gas at 23). Let's check each:

• Carbon tetrachloride: melting point -22.9°C <23°C → liquid at 23°C (eliminate A)
• Cetyl alcohol: melting point 49.3°C >23°C → solid at 23°C. Density 0.811 g/cm³ < water's density (1 g/cm³) → floats.
• Dichlorobenzene: melting point 53.5°C >23°C → solid. Density 1.25 g/cm³ >1 → sinks (eliminate C)
• Sulfur hexafluoride: melting point -64°C <23°C → gas or liquid? Boiling point -50.8°C <23°C → gas at 23°C (eliminate D)

Step2: Check density and state

Cetyl alcohol: solid (mp 49.3>23) and density 0.811<1 → floats. Others don't meet both.

Answer:

B. cetyl alcohol