Which substance chars when warmed with conc. ${\mathrm{H}}_2{\mathrm{SO}}_4$ ?

 Sulphuric acid is the strong dehydrating agent and one of the most important industrial chemicals worldwide.

When conc. ${\mathrm{H}}_2{\mathrm{SO}}_4$ Comes in contact with sugar, it becomes black due to dehydration. The sulphuric acid dehydrates the sugar (carbohydrate), removes the hydrogen and oxygen atoms releasing water as a product and carbon is left behind. ${\mathrm{C}}_{12}{\mathrm{H}}_{22}{\mathrm{O}}_{11}\stackrel{\text{ conc. }{\mathrm{H}}_2{\mathrm{SO}}_4}{⟶}12\mathrm{C}+11{\mathrm{H}}_2\mathrm{O}$

The charring reaction of carbohydrates with concentrated sulphuric acid is one of the confirmation of the dehydrating power of ${\mathrm{H}}_2{\mathrm{SO}}_4$.

In other reactions, sulphur does not decrease its oxidation state so ${\mathrm{H}}_2{\mathrm{SO}}_4$ does not act as oxidizing agent.

Hence the correct answer is (D) Carbohydrate.