Which of the following gases would be expected to have the highest density at STP?

• A. N_2
• B. Xe
• C. O_2
• D. He

Answer: (B)

Verified step by step guidance

1. Recall that the density of a gas at STP (Standard Temperature and Pressure) can be calculated using the formula \(\rho = \frac{PM}{RT}\), where \(\rho\) is the density, \(P\) is the pressure, \(M\) is the molar mass, \(R\) is the gas constant, and \(T\) is the temperature.
2. Since all gases are at the same conditions (STP), \(P\), \(R\), and \(T\) are constants, so the density is directly proportional to the molar mass \(M\) of the gas: \(\rho \propto M\).
3. Determine the molar masses of the gases given: \(N_2\) (about 28 g/mol), \(O_2\) (about 32 g/mol), \(He\) (about 4 g/mol), and \(Xe\) (about 131 g/mol).
4. Compare the molar masses to identify which gas has the highest molar mass, as this gas will have the highest density at STP.
5. Conclude that the gas with the highest molar mass, and therefore the highest density at STP, is the correct answer.