What is the product of decarboxylation of anhydrous sodium benzoate?

An ionic compound is formed by elements X and Y. Element Y forms a face-centered cubic (FCC) lattice, and element X occupies one-third of the tetrahedral voids. What is the formula of the compound?

A metal crystallizes to form simple cubic unit cell. Calculate the void volume of unit cell. [$a = 3.36 \times 10^{-8}$ cm]

Which from following ionic crystals exhibits Frenkel defect?