Gold (atomic radius =0.144 nm)crystallises in a face -centred unit cell. What is the length of a side of the cell?

Explanation

For a face-centred cubic unit cell (fcc).
`a=2 sqrt2 r=2 sqrt2 xx 0.144 nm `
`=2 xx 1.414 xx 0.144 nm=0.407 nm` therefore `4.07 xx 10^-8 cm`