To determine which substance matches Lars's observations of being solid and floating in water at room temperature [tex]\( \left(23^{\circ}C\right) \)[/tex], let's evaluate each property given:
1. Carbon tetrachloride
- Melting Point: -22.9°C
- Boiling Point: 76.7°C
- Density: 1.59 g/cm³
At 23°C:
- It is in the liquid state because 23°C falls between its melting and boiling point.
- Hence, Carbon tetrachloride does not match the observation of being a solid.
2. Cetyl alcohol
- Melting Point: 49.3°C
- Boiling Point: 344°C
- Density: 0.811 g/cm³
At 23°C:
- It is in the solid state because 23°C is below its melting point.
- Its density is 0.811 g/cm³, which is less than water's density (1 g/cm³), so it floats in water.
Cetyl alcohol matches both conditions: being solid and having a density less than water.
3. Dichlorobenzene
- Melting Point: 53.5°C
- Boiling Point: 174°C
- Density: 1.25 g/cm³
At 23°C:
- It is in the solid state because 23°C is below its melting point.
- However, its density is 1.25 g/cm³, which is greater than water's density, so it does not float in water.
4. Sulfur hexafluoride
- Melting Point: -64°C
- Boiling Point: -50.8°C
- Density: 0.00617 g/cm³
At 23°C:
- It is in the gaseous state because its boiling point is far below 23°C.
- Hence, Sulfur hexafluoride does not match the observation of being a solid.
After evaluating all options:
- Carbon tetrachloride: Liquid at 23°C (does not match)
- Cetyl alcohol: Solid at 23°C (matches) and floats in water.
- Dichlorobenzene: Solid at 23°C but sinks in water (does not match)
- Sulfur hexafluoride: Gas at 23°C (does not match)
Therefore, the substance that Lars observed is:
B. cetyl alcohol
