You are correct! The functional group found in both nucleic acids and the subset of lipids that make up biological membranes is the phosphate group (PO4)3−.

Here's why:

* Nucleic Acids: DNA and RNA are made up of nucleotides, which contain a phosphate group attached to a sugar molecule. This phosphate group is essential for forming the phosphodiester bonds that link nucleotides together to create the long chains of DNA and RNA.

* Biological Membranes: The major lipid component of biological membranes is phospholipids. These molecules have a hydrophilic head, containing a phosphate group, and two hydrophobic tails. This structure is crucial for forming the lipid bilayer that forms the foundation of cell membranes.

Let me know if you have any other questions!