Formula of oleum is
(A) \mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{7}
(B) \mathrm{H}_{2} \mathrm{SO}_{4}
(C) \mathrm{H}_{2} \mathrm{SO}_{3}
(D) \mathrm{H}_{2} \mathrm{SO}_{5}
Formula of oleum is
(A) \mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{7}
(B) \mathrm{H}_{2} \mathrm{SO}_{4}
(C) \mathrm{H}_{2} \mathrm{SO}_{3}
(D) \mathrm{H}_{2} \mathrm{SO}_{5}

Correct option is (A) \mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{7}
Oleum, or fuming sulfuric acid, is a solution of various compositions of sulfur trioxide in sulfuric acid, or sometimes more specifically to disulfuric acid (also known as pyrosulfuric acid