Match List I with List II and select the correct answer using the code given below the Lists : List I (Pigment in paint) A. Natural pigment B. Synthetic pigment C. Reactive pigment D. Inert pigment List II (Example) 1. Chalk 2. White lead 3. Red lead 4. Titanium dioxide Code :

Correct — A, A-1, B-2, C-3, D-4. Paint pigments are grouped by where they come from and how they behave in the film. Chalk, natural calcium carbonate quarried and ground, is the natural pigment, so A goes with 1. White lead, basic lead carbonate, has to be manufactured by the corrosion of lead sheet and is the classic synthetic pigment, so B goes with 2. Red lead, Pb3O4, is the reactive pigment: in an oil primer it reacts with the vehicle to form lead soaps and passivates the steel beneath, which is why it was the standard anti-corrosive primer for structural steel. Titanium dioxide is chemically inert, does not react with the vehicle or with pollutants and does not darken, which is exactly why it replaced white lead as the principal white, so D goes with 4.

• (b)A-1, B-3, C-2, D-4 — This swaps red lead and white lead. Red lead is the reactive pigment of anti-corrosive primers, and white lead the manufactured white, so pairing B with 3 and C with 2 reverses both.
• (c)A-4, B-3, C-2, D-1 — This makes titanium dioxide the natural pigment and chalk the inert one. Titanium dioxide is manufactured from ilmenite or rutile ore by the sulphate or chloride process, so it belongs on the synthetic and inert side, not the natural one.
• (d)A-4, B-2, C-3, D-1 — This keeps two pairings right but starts by calling titanium dioxide natural and chalk inert. Chalk is dug from the ground and used as it is, which is the definition of a natural pigment.

A paint has four functional parts. The binder, or vehicle, forms the film; the solvent, or thinner, controls flow and evaporates; the pigment gives colour and opacity; and additives adjust drying, skinning and flow. Pigments themselves divide by origin into natural ones dug and ground, such as chalk and the ochres, and synthetic ones manufactured, such as white lead and titanium dioxide. They also divide by behaviour into reactive pigments, which take part in chemistry inside the film to inhibit corrosion, and inert pigments, which do not.

The list mixes two different classification axes, which is what makes the matching awkward: natural against synthetic is about origin, reactive against inert is about behaviour. Sort the four examples on both axes and the code assembles itself. Chalk is the only quarried material on the list. Red lead is the only one associated with rust prevention. Titanium dioxide is famous for being inert and non-toxic, which is the reason it displaced white lead across the paint industry once lead's toxicity was recognised; white lead is now banned or tightly restricted in household paint in most countries, including India.

• A paint consists of binder, solvent, pigment and additives.
• Chalk is natural calcium carbonate, used ground as a natural pigment and extender.
• White lead, basic lead carbonate, is manufactured, and is the classic synthetic white pigment.
• Red lead, Pb3O4, is a reactive pigment that passivates steel in anti-corrosive primers.
• Titanium dioxide is chemically inert and non-toxic, and replaced white lead as the standard white.

• Calling titanium dioxide a natural pigment because rutile is a mineral; the pigment is manufactured from the ore.
• Swapping red lead and white lead, which the second option is designed to catch.
• Treating chalk as inert filler only and missing that it is also the natural pigment on this list.

A four-by-four matching item that mixes two classification axes. Fixing the two easiest pairs first cuts the options down to one.

• practice — not a real PYQ

  Which one of the following was traditionally used as an anti-corrosive primer pigment on structural steel?

  • (a)Chalk
  • (b)Red lead
  • (c)Titanium dioxide
  • (d)Lamp black

  Answer(b) Red lead — it reacts with the oil vehicle and passivates the steel surface.

• practice — not a real PYQ

  The pigment that largely replaced white lead in household paints is

  • (a)zinc chromate
  • (b)titanium dioxide
  • (c)red ochre
  • (d)barium sulphate

  Answer(b) titanium dioxide — it is opaque, inert and non-toxic.