Copper crystallises in fcc with a unit cell length of $361 \mathrm{pm}$. What is the radius of copper atom ?

In a FCC unit cell the relationship between radius(r) and edge length(a) is mathematically given as $\mathrm{r}=\frac{\mathrm{a}}{2\sqrt{2}}$

It is provided in the question that edge length is $\mathrm{a}=361\mathrm{pm}$.

Substituting this value in equation and solving we get,

$r=\frac{361}{2\sqrt{2}}$

$\mathrm{r}=127 \mathrm{pm}$

Hence, the required answer is $127 \mathrm{pm}$.