CO2 is the gas which has high density of 0.715/L at STP.
Step-by-step explanation:
PV=nRT
at STP,
P,T=constant
V=Km/M
1/K=m/V*1/M=S*1/M
therefore,
The molar mass is more, as well as the density is also greater
Hence Only CO2 has greater mass and greater density.