Alkyd resins are produced by reacting a polybasic acid (e.g., phthalic anhydride) with a polyhydric alcohol (e.g., glycerol). Identify the correct product class.

Introduction / Context:
Polycondensation reactions between polybasic acids and polyhydric alcohols yield a family of coating resins whose performance can be tuned by oil modification and monomer selection. Recognising this chemistry is essential in paints, varnishes, and coil-coating industries.

Given Data / Assumptions:

• Polybasic acid example: phthalic anhydride.
• Polyhydric alcohol example: glycerol (triol).
• Resulting resin class is tailored for coatings and varnishes.

Concept / Approach:
Alkyds are oil-modified polyesters formed by condensation of polyacids (or anhydrides) with polyols, often incorporating fatty acids or oils to enhance flexibility, flow, and drying characteristics. While unsaturated/saturated polyesters are also formed via acid-alcohol condensation, the term “alkyd” specifically denotes the oil-modified polyester systems widely used in solvent-borne and water-reducible coatings.

Step-by-Step Solution:
Map the generic reaction: polyacid + polyol → polyester backbone.Recognise the coatings context and oil modification → alkyd resin.Exclude other classes that do not match this exact industrial nomenclature.

Verification / Alternative check:
Coatings textbooks list alkyds as phthalic anhydride–glycerol based resins, frequently modified with drying oils for oxidative cure.

Why Other Options Are Wrong:
Unsaturated polyester: used for FRP with styrene crosslinking; different usage focus.Saturated polyester: film/engineering plastics; not termed “alkyd”.Amino resins: urea/melamine–formaldehyde, distinct chemistry.

Common Pitfalls:
Equating any polyester from acid-alcohol condensation with “alkyd”. Oil modification and coatings context define alkyds.

Final Answer:
Alkyd resins