Question

Assertion: Both Frenkel and Schottky defects are stoichiometric defects. Reason: Both defects change the density of the crystalline solid.

• A. Both Assertion and Reason are false.
• B. Assertion is true, but Reason is false.
• C. Both Assertion and Reason are true. The reason is the correct explanation of Assertion.
• D. Both Assertion and Reason are true. The reason is not the correct explanation of Assertion.

Answer 1

The correct option is B

Assertion is true, but Reason is false.

The explanation for Assertion statement

Stoichiometric defects

• “These are the point defects that do not disturb the stoichiometry of the solid.”
• Another name for this defect is intrinsic or thermodynamic defects.
• Schottky and Frenkel's defects are both stoichiometric defects.

Frenkel defect

• “This defect is shown by ionic solids. The smaller ion (usually cation) is dislocated from its normal site to an interstitial site.”

Schottky defect

• In ionic solids, it's basically a vacancy defect.
• The number of missing anions and cations must be equal to maintain electrical neutrality.

The explanation for Reason statement

• In the Frenkel defect, density is not changed.
• The Schottky defect decreases the density of the substance.
• So, the reason statement is incorrect.

So, the assertion is true but the reason is false. Hence, option (B) is the correct answer.