Which relationship is different? monosaccharide / polysaccharide phospholipid / lipids amino acid / protein nucleotide / nucleic acid?

The correct answer is phospholipid / lipids.

All of the pairs represent the combination of macromolecules with their basic units.

In the case of lipids, basic building blocks are free fatty acids, not phospholipids. Phospholipids are a class of lipids composed of two hydrophobic fatty acid "tails" and a hydrophilic "head" consisting of a phosphate group which are joined together by a glycerol molecule.