Among the following which one is not a redox reaction
| A. |
`CaCO_3 rarr CaO + CO_2` |
 |
| B. |
`Na + H_2O rarr NaOH +1/2H_2` |
| C. |
`MnCl_3rarrMnCl_2 +1/2 Cl_2` |
| D. |
`O_2 + 2H_2 rarr 2H_2O` |
Redox reaction means, the reaction in which oxidation as well as reduction takes place simultaneously.
In this reaction there is no change in oxidation number of any atom. Hence this reaction is not a redox reaction.