Molten NaCl is doped with 0.1 moles of AlF3. Number of cationic voids created are

Charge on Al+3  ion=+3Charge on Na+  ion=+1For every one Al+3 ion doped, three Na+ ions leave the lattice.  One of three voids vacated by Na+ ions will be occupied by Al+3.∴ effectively 2 cationic voids are developed. 0.1 moles of AlF3. … 0.3 moles of Na+ ions leave the lattice …. 0.2 moles of cationic voids.