Which defect causes a decrease in the density of a crystal?

Which of the following compounds is likely to show both Frenkel and Schottky defects in its crystalline form?

The formula of nickel oxide with metal deficiency defect in its crystal is $Ni_{0.98}O$. The crystal contains $Ni^{2+}$ and $Ni^{3+}$ ions. The fraction of nickel existing as $Ni^{2+}$ ions in the crystal is

Assertion : Due to Frenkel defect,there is no effect on the density of the crystalline solid.
Reason : In Frenkel defect,no cation or anion leaves the crystal.

Assertion : No compound has both Schottky and Frenkel defects.
Reason : Both defects change the density of the solid.

Which type of defect is observed in $AgBr$?