Final answer:
The mass of carbon dioxide gas in the container is 17.25 g.
Step-by-step explanation:
To find the mass of carbon dioxide gas in the container, we can set up a proportion using the given information. If the volume of the container with CO2 gas is half the volume of the container with O2 gas, then the mass of CO2 gas will also be half the mass of O2 gas. So, the mass of carbon dioxide gas in the container would be 34.5 g / 2, which is 17.25 g.