The defect that arises when smaller cations move into interstitial sites in a crystal lattice is known as ..............

Which statement is correct regarding the $F$-center?

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:

The formula of nickel oxide is $Ni_{0.98}O_{1.00}$. What is the approximate percentage of $Ni^{2+}$ in it?

If molten $NaCl$ contains $SrCl_2$ as impurity,crystallization can generate

Which of the following statements is $WRONG$?