A phosphodiester bond is present in

The correct option is Nucleic acids in a nucleotide.

To determine where a phosphodiester bond is present, let us examine the typical chemical linkages found in each of the given biomolecules:
1. Monosaccharides in a polysaccharide: Monosaccharide units (such as glucose) are linked together by covalent glycosidic bonds to form complex carbohydrates or polysaccharides.
2. Amino acids in a polypeptide: Amino acids are linked linearly by peptide bonds (amide linkages) to form polypeptide chains and proteins.
3. Fatty acids in a diglyceride: Fatty acids are bonded to a glycerol backbone through ester bonds.
4. Nucleic acids: Nucleic acids (DNA and RNA) are polymers composed of repeating monomeric units called nucleotides. Inside a nucleic acid chain, adjacent nucleotides are covalently joined by a phosphodiester bond. This bond specifically links the 3' hydroxyl (-OH) group of the pentose sugar of one nucleotide to the 5' phosphate group of the next nucleotide, forming the sugar-phosphate backbone of the nucleic acid.

Consequently, phosphodiester bonds are the key structural linkages characteristically found in nucleic acids.