Melamine–formaldehyde (MF) resin has very high anti-tacking and excellent hardness. In industrial practice, MF resins are used for many applications; identify the application from the list below for which MF resin is generally not used.

Introduction / Context:
Melamine–formaldehyde (MF) resins are thermosetting polymers valued for their high surface hardness, gloss retention, stain resistance, heat resistance, and very good anti-tacking behavior. They cure to a cross-linked network that is dimensionally stable and electrically insulating. This question asks you to separate common, well-documented MF applications from an option that is not a typical or mainstream use in materials engineering practice.

Given Data / Assumptions:

• MF resins are cross-linked thermosets once cured.
• They exhibit high hardness, abrasion resistance, electrical insulation, and chemical resistance.
• We consider standard, widely taught industrial uses.

Concept / Approach:
MF resins are ubiquitous in decorative laminates (as the hard, transparent overlay), electrical insulating components (switchgear, sockets, appliance housings), tableware, and as crosslinkers in coatings and textiles. MF-based resins have also been formulated as retanning agents in leather processing. By contrast, “strengthening of plaster of Paris (POP)” is not a textbook or mainstream application for MF; gypsum systems are more commonly modified with polymer latexes (e.g., polyvinyl acetate, acrylics), fibers, or retarders/accelerators rather than melamine cross-linkers.

Step-by-Step Solution:

Verification / Alternative check:
Materials handbooks and product literature consistently associate MF with laminates (HPL), molding compounds for electrical parts, dinnerware, and crosslinking agents; POP systems are improved with different polymer modifiers, not MF networks.

Why Other Options Are Wrong:

• Electrical insulation: MF molding compounds are standard insulators.
• Tanning of leather: melamine resin retanning agents exist in practice.
• Decorative laminates: MF is the classic overlay/crosslinker.
• Tableware glazing/surfaces: melamine ware is widely known.

Common Pitfalls:
Assuming any thermoset “strengthens” all minerals; polymer–gypsum synergy depends on chemistry and water compatibility.

Final Answer:
Strengthening of plaster of Paris