The correct answer is: A. Not soluble in water
Resins are a natural or synthetic solid or semisolid adhesive or plastic substance of plant or animal origin, typically yellow or brown and brittle when dry. They are insoluble in water, but soluble in organic solvents such as alcohol, ether, and benzene. Resins are used in a variety of products, including varnishes, paints, adhesives, and plastics.
Option B is incorrect because resins are not soluble in spirit. Spirit is a type of alcohol, and alcohol is a solvent for resins.
Option C is incorrect because resins are not the only thing that is used in varnishes. Varnishes are made from a variety of ingredients, including resins, solvents, and pigments.
Option D is incorrect because resins are not left behind on the evaporation of oil. When oil evaporates, it leaves behind a residue of carbon. This residue is not a resin.