To determine the most likely identity of the substance Lars observes, we need to analyze the properties of each substance given in the table and compare them with the observations. Our goal is to identify which substance is a solid and floats in water at room temperature (23°C). A substance floats in water if its density is less than 1 g/cm³.
Here’s a step-by-step analysis of each substance:
1. Carbon Tetrachloride:
- Melting Point: -22.9°C
- Boiling Point: 76.7°C
- Density at Room Temperature: 1.59 g/cm³
At 23°C:
- Carbon tetrachloride is a liquid because 23°C is between its melting point and boiling point.
- Its density (1.59 g/cm³) is greater than 1 g/cm³, so it would not float in water.
2. Cetyl Alcohol:
- Melting Point: 49.3°C
- Boiling Point: 344°C
- Density at Room Temperature: 0.811 g/cm³
At 23°C:
- Cetyl alcohol is a solid because 23°C is below its melting point.
- Its density (0.811 g/cm³) is less than 1 g/cm³, so it would float in water.
3. Dichlorobenzene:
- Melting Point: 53.5°C
- Boiling Point: 174°C
- Density at Room Temperature: 1.25 g/cm³
At 23°C:
- Dichlorobenzene is a solid because 23°C is below its melting point.
- Its density (1.25 g/cm³) is greater than 1 g/cm³, so it would not float in water.
4. Sulfur Hexafluoride:
- Melting Point: -64°C
- Boiling Point: -50.8°C
- Density at Room Temperature: 0.00617 g/cm³
At 23°C:
- Sulfur hexafluoride is a gas because 23°C is above its boiling point.
- Its density (0.00617 g/cm³) is less than 1 g/cm³, but it is not a solid at 23°C, so it does not fit the criteria for Lars' substance.
Based on the observations:
- The substance must be a solid at 23°C.
- The substance must float in water due to its density being less than 1 g/cm³.
Conclusion:
The most likely identity of the substance Lars observes is cetyl alcohol (Answer: B).
