Chemistry - Metallurgy Question with Solution | TestHub

Which method of purification is represented by the following equation.

$\text{Ni}+4 \text{CO}\underset{\text{Δ}}{\overset{70{}^{\text{o}}\text{C}}{\to }}\text{Ni}{\left(\text{CO}\right)}_4\underset{\text{Δ}}{\overset{180{}^{\text{o}}\text{C}}{\to }}\text{Ni}+4 \text{CO}$