What is the smallest pigment molecule?

• A. Carbon
• B. Titanium dioxide
• C. Iron oxide
• D. Organic pigments

Answer: (A)

The key idea is pigment composition and molecular size. Elemental carbon used as a pigment (carbon black) is essentially carbon in its simplest form—an element without additional atoms bonded to make a compound. That makes its pigment units the smallest in terms of atomic complexity. In contrast, titanium dioxide and iron oxide are inorganic compounds with defined formulas (TiO2 and Fe2O3), which involve more atoms per unit, and organic pigments are large carbon-based molecules with even higher molecular weights. So elemental carbon stands out as the smallest pigment molecule among the options.