Q.Classify each of the following as a substitutional or an interstitial solid solution, with a reason:

A solid solution is a homogeneous solid mixture formed when a solute dissolves throughout the crystal lattice of

a solid solvent, and the way the solute atoms fit into that lattice determines which of two types results.

A substitutional solid solution forms when solute atoms, similar enough in size and chemical character to the

solvent atoms, directly replace solvent atoms at regular lattice sites — brass (zinc atoms replacing copper atoms

in the copper lattice) and bronze (tin in copper) are classic examples, and this substitution is favoured when the

two atoms' sizes differ by no more than about 15% (the Hume-Rothery size rule).

An interstitial solid solution forms instead when the solute atoms are considerably smaller than the solvent

atoms, small enough to occupy the empty interstitial gaps between solvent atoms rather than replacing them at all

— steel (small carbon atoms wedged between the iron atoms of the iron lattice) is the standard example, and the …