(A) Efflorescence means spontaneous loss of water by a hydrated salt.
Conc. sulphuric acid is not efforescent. Thus, the option A is incorrect.
(B) Conc. sulphuric acid has strong affinity for water and is hygroscopic. It readily absorbs moisture. Hence, the option B is correct.
(C) Conc. sulphuric acid is strong oxidizing agent as it gives oxygen on strong heating. It oxidizes non-metals, metals above hydrogen in electrochemical series and several compounds. Hence, the option C is correct.
(D) Conc. sulphuric acid is sulphonating agent. It introduces sulphonic acid group into aromatic nucleus. Hence, option D is correct.
C6H6+HO.SO2.OH→C6H5.SO2−OH