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. primitive
B. face-centred
C. body-centred
D. end-centred

Answer

B

Explanation

`"No. of atoms in a unit cell"=("Volume of unit cell" xx "Density of unit cell")/("Molar mas of single atom")`
`=((405xx10^(-10) cm)^(3) (27 g cm^(-3)))/(28 g "mol"^(-1) //(6.023 xx1023 "mol"^(-1)))`
Hence the unit cell of face centred.