(A) $(i)$ Direct oxidation of $C$ in limited supply of oxygen or air yields carbon monoxide: $C + \frac{1}{2} O_{2} \xrightarrow{\Delta} CO$.
$(ii)$ Reduction of heavy metal oxides with carbon gives $CO$: $ZnO + C \rightarrow Zn + CO$ and $Fe_{2}O_{3} + 3C \rightarrow 2Fe + 3CO$.
$(iii)$ On a small scale,pure $CO$ is prepared by dehydration of formic acid with concentrated $H_{2}SO_{4}$ at $373 \ K$: $HCOOH \xrightarrow[\text{Conc. } H_{2}SO_{4}]{373 \ K} CO + H_{2}O$.
$(iv)$ On a commercial scale,it is prepared by the passage of steam over hot coke. The mixture of $CO$ and $H_{2}$ thus produced is known as water gas or synthesis gas: $C_{(s)} + H_{2}O_{(g)} \xrightarrow{473 \ K - 1273 \ K} CO_{(g)} + H_{2(g)}$.
When air is used instead of steam,a mixture of $CO$ and $N_{2}$ is produced,which is called producer gas: $2C_{(s)} + O_{2(g)} + 4N_{2(g)} \xrightarrow{1273 \ K} 2CO_{(g)} + 4N_{2(g)}$.
Properties and Uses: $CO$ is a colorless,odorless,and toxic gas. It acts as a powerful reducing agent and is used in the extraction of metals. Water gas and producer gas are important industrial fuels.