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

(N/A) For a face-centred unit cell $(fcc)$:
$a = 2 \sqrt{2} r$
Given that the atomic radius,$r = 0.144 \, nm$.
Substituting the value of $r$ in the formula:
$a = 2 \times 1.414 \times 0.144 \, nm$
$a = 0.407232 \, nm$
Rounding to three decimal places,the length of a side of the cell is $0.407 \, nm$.