Which one of the following reactions represents water-gas shift reaction ?

• A

  $\mathrm{CO}\left(\mathrm{g}\right) + {\mathrm{H}}_2\mathrm{O} \left(\mathrm{g}\right) \underset{\mathrm{Iron} \mathrm{chromate}}{\overset{673 \mathrm{K}}{\to }} {\mathrm{CO}}_2 + {\mathrm{H}}_2$

• B

  $\mathrm{CO}\left(\mathrm{s}\right) + {\mathrm{H}}_2\mathrm{O} \left(\mathrm{g}\right) \underset{ }{\overset{1270 \mathrm{K}}{\to }} \mathrm{CO}\left(\mathrm{g}\right) + {\mathrm{H}}_2$

• C

  ${\mathrm{CH}}_4\left(\mathrm{g}\right) + {\mathrm{H}}_2\mathrm{O} \left(\mathrm{g}\right) \underset{\mathrm{Ni}}{\overset{1270 \mathrm{K}}{\to }} \mathrm{CO}\left(\mathrm{g}\right) + 3{\mathrm{H}}_2 \left(\mathrm{g}\right)$

• D

  None of these