Explain stoichiometric defects shown by non-ionic solids.

(N/A) $(i)$ Vacancy Defect: When some of the lattice sites are vacant,the crystal is said to have a vacancy defect. This results in a decrease in the density of the substance.
$(ii)$ Interstitial Defect: When some of the constituent particles (atoms or molecules) occupy an interstitial site,the crystal is said to have interstitial defects. The density of the crystal increases due to this defect.