The structure of MgO is similar to NaCl the number of next nearest neighbour of Mg is – a) 4 b) 6 c) 12 d) 8 Please answer with details and what does it mean by “next nearest neighbour’’?

Hello Student,

Nearest neighbours to a FCC latice would be 12 w.r.t a face centre or corner at a distance of a/√2.

For Next nearest neighbours, count the Nearest neighbours with respect to corner atom as you would do in simple cubic which would come out to be 6 at a distance of a.

Please look at the image carefully, it will make your concept clear.