${\mathrm{C}}_{12}{\mathrm{H}}_{22}{\mathrm{O}}_{11}\stackrel{{\mathrm{H}}_2{\mathrm{SO}}_4}{⟶}{\mathrm{H}}_2\mathrm{O}+\mathrm{A}\stackrel{{\mathrm{H}}_2{\mathrm{SO}}_4}{⟶}\mathrm{B}+\mathrm{C}+{\mathrm{H}}_2\mathrm{O}$ 
If the compound C is an oxide of group VIA element, then the compound B is

1. The given reaction is the reaction between sugar and sulphuric acid
2. When concentrated sulphuric acid is added to sugar, it dehydrates the sugar to form carbon dioxide and water along with the liberation of sulphur dioxide SO₂ gas.
3. This reaction is an example of a dehydration reaction because sulphuric acid is used to dehydrate sugar.

C₁₂H₂₂O₁₁(s)+Conc.H₂SO₄(aq)→SO₂(g)+H₂O(g)+CO₂(g)

The product of the given reaction is Sulphur dioxide SO₂, steam H₂O, and carbon dioxide gas CO_2.