Assertion: Metal excess defect is a non-stoichiometric defect.
Reason: F-centers are occupied by paired electrons.
Answer & explanation
Correct answer: option 2
Non stoichiometric defects: Ratio of number of cations and anions is not maintained as shown by chemical formula.
Metal excess defect is a non-stoichiometric defect which is created by anion vacancy or extra cation in the interstitial sites.
It develops a hole trapping electron e-.
F-centers are occupied by paired electrons which imparts colour to the crystals like NaCl, KCl and LiCl.