Here are the root names for hydrocarbons containing two, three, and four carbon atoms:

* Two carbon atoms: Eth-

* Three carbon atoms: Prop-

* Four carbon atoms: But-

These prefixes are used in naming various hydrocarbons, including alkanes, alkenes, alkynes, and cyclic hydrocarbons. For example:

* Ethane (C₂H₆) - an alkane with two carbon atoms

* Propene (C₃H₆) - an alkene with three carbon atoms

* Butyne (C₄H₆) - an alkyne with four carbon atoms