Discussion
The common shapes of crystalline pigments are :
(a) Spherical
(b) Cubic
(c) Rectangular
(d) Needle-shaped
Choose the correct answer from the options given below :
Answer: D
The common shapes of crystalline pigments are cubic, rectangular and needle-shaped.
Pigment particles are crystals, and the crystal habit decides their shape: blocky cubic or prismatic forms, rectangular plates or blocks, and long needles (acicular forms) are all met in paint and ink pigments. A near-spherical particle is not a crystal habit. An early electron-microscope study (Nature, 1947) found that among commonly used pigments only carbon particles are spherical, and other inorganic pigments give crystalline particles. So (a) does not belong in the list, which leaves (b), (c) and (d).
Options A, B and C each include 'spherical' and so are wrong. This is a textbook-style list; sources classify shapes under slightly different names (prismatic, acicular, lamellar), and we read 'rectangular' with the key.
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