CO2 is carbon dioxide.
Chemical symbols describe the atomic makeup of a substance. Every known atom has a 1-3 letter abbreviation, which you can look up on a periodic table. In the case of CO2, C tells you that there is...
Cobalt II Chlorate
2 player coop duh
Yes, Mercenaries 2: World in Flames supports cooperative online play. Cooperative play is limited to two players.