The cubic unit cell of Al (molar mass 27 g `"mol"^(-1)` ) has an edge length of 405 pm. Its density is `2.7gcm^(-3)` . The cubic unit cell is :

Options

A. face centred
B. body centred
C. primitive
D. edge centre

Explanation

Density `(rho) = (ZxxM)/(a^(2)xxN_(0))`
`2.7=(Zxx27)/((405xx10^(-10))xx6.023xx10^(23))`
`Z=(2.7xx(405)^(2)xx10^(-30)xx6.023xx10^(22))/(27)`=4= no. of atoms per unit cell. For face centred cubic unit cell, number of atoms are 4.