Question

Which of the following gases has the highest density at STP?

• A. \( \text{CO}_2 \)
• B. \( \text{O}_2 \)
• C. \( \text{N}_2 \)
• D. \( \text{CH}_4 \)

Hint:

Remember: At STP, the density of a gas is directly proportional to its molar mass. Higher molar mass means higher density.

Answer 1

The Correct Option is A

Step 1: Recall the formula for density of a gas
The density \( \rho \) of a gas at STP (Standard Temperature and Pressure) is given by: \[ \rho = \frac{\text{Molar mass}}{\text{Molar volume at STP}} \] At STP, the molar volume of any ideal gas is approximately \( 22.4 \, \text{L/mol} \).
Step 2: Compare the molar masses of the gases
- Molar mass of \( \text{CO}_2 \) = \( 12 + 2 \times 16 = 44 \, \text{g/mol} \),
- Molar mass of \( \text{O}_2 \) = \( 2 \times 16 = 32 \, \text{g/mol} \),
- Molar mass of \( \text{N}_2 \) = \( 2 \times 14 = 28 \, \text{g/mol} \),
- Molar mass of \( \text{CH}_4 \) = \( 12 + 4 \times 1 = 16 \, \text{g/mol} \).
Step 3: Determine the gas with the highest density
Since the density of a gas is directly proportional to its molar mass at STP, \( \text{CO}_2 \) has the highest molar mass and hence the highest density at STP. Answer: Therefore, \( \text{CO}_2 \) has the highest density at STP. So, the correct answer is option (1).