Which is not a macromolecule fat , protein, nucleic acid, water

water is not a macromolecule

Explanation: fatty acids such as stearic, palmitic, linoleic are large compared with water (50 or so atoms compared with the 3 of water) but still small c.f. proteins and nucleic acids which may have 1000s or millions of atoms. As trigycerides, fats may have >200 atoms.

While nucleic acids and proteins are definitely macromolecules, there may be different opinions as to whether fats are considered macromolecules.

when a reversible reaction is occurring in both directions at the same rate; the products and reactants do not change in concentration. a chemical reaction where the compound is broken into its constituent parts.