(a) NaCl has fcc unit cell nearest neighbour distance in fcc unit cell =a√2 So, option (a) is incorrect. (b) Total volume of a unit cell in ccp=(2√2r)3 So, option (b) is incorrect. (c) Packing fraction of bcc unit cell =68.04% Packing fraction of fcc unit cell =74% So, packing fraction of fcc is greater than that of bce unit cell. So, option (c) is also incorrect. (d) For a bcc, nearest neighbour distance =a√3∕2. Since, CsCl is a body centered cubic crystal, so the nearest neighbour distance will be equal to a√3∕2