Sulfuric acid is a strong hygroscopic substance – Proof:
When concentrated H2SO4 is added to sugar, the H2SO4 absorbs all the water content of the sugar and the sugar turns into black carbon.
C12H22O11 + Conc. H2SO4 = 12C + [11H2O + H2SO4 ]
This shows that sulfuric acid is a very strong hygroscopic substance.