Choose from: (I). atomic group. (II). thermal group. (III). molecular group. (IV). functional group.
Given those answer options, answer the question: Answer the following question given this paragraph: With over twenty million known organic compounds in existence, it would be very challenging to memorize chemical reactions for each one. Fortunately, molecules with similar functional groups tend to undergo similar reactions. A functional group is defined as an atom or group of atoms within a molecule that has similar chemical properties whenever it appears in various compounds. Even if other parts of the molecule are quite different, certain functional groups tend to react in certain ways. Q: What is the germ for a group of atoms within a molecule that reacts similarly anywhere it appears in different compounds? A:
A:
(IV).