Question

Assertion (A) : The density of crystal having Schottky defect is lowered.
Reason (R) : The crystals suffering from Schottky defect have same number of cations and anions missing from their normal lattice sites.

• A. If both (A) and (R) are correct, and (R) is the correct explanation of (A)
• B. If both (A) and (R) are correct, but (R) is not the correct explanation of (A)
• C. If (A) is correct, but (R) is incorrect
• D. If (A) is incorrect. but (R) is correct
• E. If both (A) and (R) are incorrect

Answer 1

The correct option is A If both (A) and (R) are correct, and (R) is the correct explanation of (A)

Schottky defect is a defect which is produced when one cation and anion are missing from their respective positions leaving behind a pair of holes. The crystal as a whole remains neutral because the number of missing positive ions (cations) and negative ions (anions) is the same.
Consequences of Schottky defect: Density of the crystal decreases. The crystal begins to conduct electricity to small extent by ionic mechanism. The presence of too many voids lowers the lattice energy or the stability of the crystal. Hence, both assertion and reason are correct and reason is the correct explanation for assertion.