The appearance of colour in solid alkali metal halides is generally due to

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:

Identify the incorrect statement regarding crystals having $Frenkel$ defect.

The flame colours of metal ions are due to

Which relationship is correct regarding the coordination number and the size of cations and anions in ionic compounds exhibiting Schottky defect?

When $SrCl_2$ is added to molten $NaCl$ and crystallized,the defect formed is ........