Schottky defect is generally observed in which of the following?

Given below are two statements.
Statement $I:$ Frenkel defects are vacancy as well as interstitial defects.
Statement $II:$ Frenkel defect leads to colour in ionic solids due to presence of $F$-centres.
Choose the most appropriate answer for the statements from the options given below:

The flame colours of metal ions are due to

Which of the following statements is $WRONG$?

When $AgCl$ is doped with $10^{-4} \, \text{mole percent}$ $RuCl_3$,what will be the concentration of cationic vacancies per mole of $AgCl$?

Identify the type of defect from the following in stainless steel.