when impure nikel is heated in pesence of CO at 330 -350 K it froms volatine nikel tetracarbonny leaving behind the ipurities . The nikel tetracarbony thus obtained is then Heated tohigher temperature (450 -470 K) ,then it undergoes thermal decomposition to give pure nikel .
`underset(("Impure") +4CO overset(330-250 K)to underset( "Ninkel tetracarbondy") (Ni(CO)_(4))`
`Ni(CO)_(4) overset(450-470 )to underset("Nikel") Ni +4CO `
