How does the density of a crystal change in Schottky defect and Frenkel defect?

Which among the following statements is $NOT$ true about Frenkel defect?

Which of the following statements is $WRONG$?

Which of the following is non-stoichiometric?

Given below are two statements: one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R).$
Assertion $(A):$ In a particular point defect,an ionic solid is electrically neutral,even if few of its cations are missing from its unit cells.
Reason $(R):$ In an ionic solid,Frenkel defect arises due to dislocation of cation from its lattice site to interstitial site,maintaining overall electrical neutrality.
In the light of the above statements,choose the most appropriate answer from the options given below:

Why does white $ZnO_{(s)}$ become yellow upon heating?