Molar mass of nitrobenzene = 123 Equivalent mass of nitrobenzene
$\text{=}\frac{\text{Molecular}\text{mass}}{\text{6}}$
$=\frac{123}{6}=20.5$
Number of equivalents of nitrobenzene
$\text{=}\frac{\text{Mass}}{\text{Equivalent}\text{mass}}$
$=\frac{12.3}{20.5}=0.6$
Amount of charge required $=0.6\times 96500=57900$ Coulomb
Amount of charge required when current efficiency is 50%
$=2\times 57900$
$\text{=}\text{115800}\text{C}$