Benzene on treatment with a mixture of conc. $$\mathrm{HNO_3}$$ and conc. $$\mathrm{H_2SO_4}$$ at $$100^{\circ}\mathrm{C}$$ gives

This is nitration of benzene. Under ordinary nitrating conditions, benzene first forms nitrobenzene. At about $$100^{\circ}\mathrm{C}$$ with the nitrating mixture, further nitration can occur, and since the $$-\mathrm{NO_2}$$ group is deactivating and meta-directing, the second nitro group enters the meta position. So the product is $$m\text{-dinitrobenzene}$$. On checking the options, this matches option $$\text{C}$$.