The reagent, from the following, which converts benzoic acid to benzaldehyde in one step is

When benzoic acid is heated with formic acid in presence of $\mathrm{Mno}$, benzaldehyde is obtained.

The reaction is given below, along with benzaldehyde, carbondioxide and water are also obtained.

${\mathrm{C}}_6{\mathrm{H}}_5\mathrm{COOH}+\mathrm{HCOOH}\underset{\mathrm{Heat}}{\overset{\mathrm{MnO}}{\to }}{\mathrm{C}}_6{\mathrm{H}}_5\mathrm{CHO}+{\mathrm{CO}}_2+{\mathrm{H}}_2\mathrm{O}$