Carbon dioxide is lighter than air.

Answer

To determine whether carbon dioxide (CO2) is lighter or heavier than air, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Composition of Air**:
- Air is primarily composed of nitrogen (N2) and oxygen (O2). The approximate composition is about 78% nitrogen and 21% oxygen, with trace amounts of other gases.

2. **Determine the Molecular Mass of Carbon Dioxide (CO2)**:
- The molecular formula for carbon dioxide is CO2, which means it consists of one carbon atom and two oxygen atoms.
- The atomic mass of carbon (C) is 12 g/mol.
- The atomic mass of oxygen (O) is 16 g/mol. Since there are two oxygen atoms in CO2, we calculate the total mass of oxygen as follows:
\[ \text{Total mass of oxygen} = 2 \times 16 = 32 \text{ g/mol} \]
- Now, we can calculate the molecular mass of CO2:
\[ \text{Molecular mass of CO2} = \text{mass of C} + \text{mass of O} = 12 + 32 = 44 \text{ g/mol} \]

3. **Determine the Molecular Mass of Air Components**:
- The molecular mass of nitrogen (N2) is calculated as follows:
\[ \text{Molecular mass of N2} = 2 \times 14 = 28 \text{ g/mol} \]
- The molecular mass of oxygen (O2) is:
\[ \text{Molecular mass of O2} = 2 \times 16 = 32 \text{ g/mol} \]

4. **Compare the Molecular Masses**:
- Now, we compare the molecular mass of CO2 (44 g/mol) with the average molecular masses of the components of air (N2: 28 g/mol and O2: 32 g/mol).
- Since 44 g/mol (CO2) is greater than both 28 g/mol (N2) and 32 g/mol (O2), we conclude that carbon dioxide is heavier than air.

5. **Conclusion**:
- Therefore, the statement "Carbon dioxide is lighter than air" is incorrect. Carbon dioxide is actually heavier than air.