In the reaction 

The equivalent weight of Nitrobenzene is

Six hydrogen atoms are required for the reduction of one molecule of nitrobenzene to aniline. 

Balance chemical reaction

${\mathrm{C}}_6{\mathrm{H}}_5{\mathrm{NO}}_2+6\left[\mathrm{H}\right]\to {\mathrm{C}}_6{\mathrm{H}}_5{\mathrm{NH}}_2+2{\mathrm{H}}_2\mathrm{O}$

So, the equivalent weight of Nitrobenzene is $\mathrm{M}/6$.

Therefore, option D is correct.