Compounds. There are more carbon compounds than there are compounds of all other elements combined. The study of carbon compounds, both natural and synthetic, is called organic chemistry. Plastics, foods, textiles, and many other common substances contain carbon.
backplane is the shared capacity between interfaces on a switch switch fabric is also the shared capacity between interfaces on a switch and can also be the shared capacity between interfaces on multiple switches using some sort of interconnect, typically vendor specific.
Which means the backplane can only accommodate the traffic from six ports before it's saturated (or over subscribed). Hence the 2:1 over subscription. If you're expecting all 12 ports on this switch to be fully utilized, this is not a good switch for you.