Which one of the following methods is used to prepare carbon...

(a) When formic acid $\mathrm{HCOOH}$ is dehydrated with $\mathrm{H}_2 \mathrm{SO}_4$ (conc.), it gives carbon monoxide (CO)$and \mathrm{H}_2 \mathrm{O}$ as : \mathrm{HCOOH}+\mathrm{H}_2 \mathrm{SO}_4 \text { (conc.) } \longrightarrow \mathrm{CO}+\mathrm{H}_2 \mathrm{O}+\mathrm{H}_2 \mathrm{SO}_4 But the above process is not used on commercial scale. (b) Direct oxidation of carbon in limited supply of oxygen can give $\mathrm{CO}$ but the process is not used on commercial scale. 2 \mathrm{C}+\mathrm{O}_2 \text { (limited supply) } \longrightarrow 2 \mathrm{CO} (c) When steam $\left(\mathrm{H}_2 \mathrm{O}\right)$ is passed over coke $(\mathrm{C})$, it gives $\mathrm{CO}+\mathrm{H}_2$, as : \text { Coke }(\mathrm{C})+\underset{(\text { Steam) }}{\mathrm{H}_2 \mathrm{O}} \stackrel{\Delta}{\mathrm{Ni}} \mathrm{CO}(g)+\mathrm{H}_2(g) The above process can be used to produce (CO) on commercial scale. (d) Lime stone is $\mathrm{CaCO}_3$, on heating it gives oxygen $\left(\mathrm{O}_2\right)$ and $\mathrm{CaO}$ as : \mathrm{CaCO}_3 \stackrel{\Delta}{\longrightarrow} \mathrm{CaO}+\mathrm{O}_2 Hence, option (c) is the correct answer.