Which pair of gases cannot be collected by downward delivery: SO2, NH3, CO, N2, Cl2, H2S?

• Molar mass of SO$_2$: $32.07 + 2(16.00) = 64.07 \text{ g/mol}$
• Molar mass of NH$_3$: $14.01 + 3(1.01) = 17.04 \text{ g/mol}$
• Molar mass of CO: $12.01 + 16.00 = 28.01 \text{ g/mol}$
• Molar mass of N$_2$: $2(14.01) = 28.02 \text{ g/mol}$
• Molar mass of Cl$_2$: $2(35.45) = 70.90 \text{ g/mol}$
• Molar mass of H$_2$S: $2(1.01) + 32.07 = 34.09 \text{ g/mol}$

• SO$_2$ ($64.07 \text{ g/mol}$) is denser than air ($29 \text{ g/mol}$), so it can be collected by downward delivery.
• NH$_3$ ($17.04 \text{ g/mol}$) is less dense than air, so it cannot be collected by downward delivery.
• CO ($28.01 \text{ g/mol}$) is less dense than air, so it cannot be collected by downward delivery.
• N$_2$ ($28.02 \text{ g/mol}$) is less dense than air, so it cannot be collected by downward delivery.
• Cl$_2$ ($70.90 \text{ g/mol}$) is denser than air, so it can be collected by downward delivery.
• H$_2$S ($34.09 \text{ g/mol}$) is denser than air, so it can be collected by downward delivery.

The question asks for the pair of gases that cannot be collected by downward delivery. This implies that for the chosen pair, neither gas should be suitable for downward delivery.

• **A. SO$_2$ and NH$_3$