What is the formula for an ethyl group?

An ethyl group, which is derived from ethane by removing one hydrogen atom, has the formula -C2H5. This structure consists of two carbon atoms and five hydrogen atoms, which is characteristic of the ethyl group.

In the context of molecular structure, the ethyl group is often represented as a substituent in organic compounds, typically attached to other groups or structures. Ethyl is part of various hydrocarbons and contributes to the properties and reactivity of the overall molecule.

The other choices do not accurately represent an ethyl group. For instance, -C2H4 represents an ethylene group (ethene), which contains a double bond between the two carbon atoms. The -CH3 corresponds to a methyl group, which has only one carbon and three hydrogens. Finally, -C3H7 defines a propyl group, which consists of three carbons, and is not related to the ethyl structure. Thus, -C2H5 is the correct representation for an ethyl group.