Formation of $Ni(CO)_4$ and its subsequent decomposition into $Ni$ and $CO$ (recycled) forms the basis of the Mond process.
$Ni + 4CO$ $\xrightarrow{T_1} Ni(CO)_4$ $\xrightarrow{T_2} Ni + 4CO$
$T_1$ and $T_2$ are:

• A
  $100 \ ^\circ C, 50 \ ^\circ C$
• B
  $50 \ ^\circ C, 100 \ ^\circ C$
• C
  $50 \ ^\circ C, 230 \ ^\circ C$
• D
  $230 \ ^\circ C, 50 \ ^\circ C$