Final answer:
The Greek prefix for the compound C2H6 is 'eth-' indicating two carbon atoms. C2H6 is called ethane, a nonpolar covalent compound, and does not have a cation.
Step-by-step explanation:
The compound C2H6 is covalently bonded and is called ethane. The Greek prefixes are used in covalent compounds to indicate the number of atoms of each element present in the compound. Since ethane has two carbon atoms, the Greek prefix used is 'eth-' derived from 'di-' indicating two carbon atoms. There is no cation in C2H6 because it is a nonpolar covalent compound, and both elements involved are nonmetals.