Step 1: Recall FCC relation between edge length and radius.
For FCC lattice:
\[
a = 2\sqrt{2}\,r
\] Step 2: Substitute the given value.
\[
a = 405\ \text{pm}
\]
\[
r = \frac{a}{2\sqrt{2}} = \frac{405}{2.828}
\] Step 3: Calculate radius.
\[
r \approx 143.2\ \text{pm}
\] Step 4: Conclusion.
The radius of the atom is 143.2 pm.