The only incorrect effect on density by the given defect in solids is — Solid State Chemistry Question

💡 Solution & Explanation

An impurity defect involves substituting an original lattice atom/ion with a different atom/ion. Depending on whether the mass of the impurity atom is lighter or heavier than the host atom it replaces, the overall density can either decrease or increase; it does not strictly "must increase". Therefore, correct answer is C.