Nickel $(Ni)$ on heating in a stream of carbon monoxide forms a volatile complex, that is nickel tetracarbonyl.
$\underset{\text{Nickel}}{\ce{Ni}}+$ $\underset{\text{Carbon
monoxide}}{\ce{HCO}}\ce{->[330-350\,K]}$ $\underset{\text{Nickel tetracarbonyl
(volatile compound)}}{\ce{[Ni(CO)4]}}$