Final answer:
(a) pyrophosphate. Without the figure provided, it's not possible to definitively identify the functional group circled on the nucleotide. However, a nucleotide is composed of a phosphate group,
Step-by-step explanation:
Nucleotides are the monomer subunits that make up nucleic acids such as DNA and RNA. Each nucleotide is composed of three components:
one or more phosphate groups, a pentose sugar (either ribose or deoxyribose), and a nitrogen-containing base (adenine, cytosine, guanine, thymine, or uracil).
When nucleotides form the sugar-phosphate backbone of a nucleic acid strand, they are connected by phosphodiester linkages, which involve the phosphate group.
In the context of DNA replication, a nucleoside triphosphate adds to the growing chain by forming a bond with the incoming nucleotide, resulting in the elimination of pyrophosphate (a molecule consisting of two phosphate groups), as the reaction leaves behind a phosphoryl group attached to the nucleotide's sugar.
If the functional group you are inquiring about in your question is associated with this release of pyrophosphate during the process of nucleic acid synthesis, the circled group would then likely be identified as a phosphoryl group rather than pyrophosphate, but without the actual figure provided, confirming the precise category of the functional group in question is not possible.
However, for further clarification, pyrophosphate refers to a molecule with two phosphate units, phosphoryl is the group single linked to the remainder of the molecule, carbonyl contains a carbon-oxygen double bond, and carboxyl is a carbon double-bonded to an oxygen and also bonded to a hydroxyl group.