Question

What is the molecular formula of Oleum?
A.$H_2{SO}_3$
B$.H_2{SO}_5$
C.$H_2{S}_2{O}_7$
D.$H_2{S}_2{O}_8$

Answer 1

Hint:You should know that oleum is a dense, corrosive mixture consisting of concentrated sulfuric acid with upto 80% of sulfur trioxide. It is also used for sulfonation processes.

Complete step by step answer:
Oleum is 100% sulfuric acid $H_2{SO}_4$containing dissolved sulfur trioxide gas ${SO}_3$. Oleum is produced by continuing to absorb ${SO}_3$ gas into a recirculating { H }_{ 2 }{ SO }_{ 4 } stream. Generally you should know that the amount of ${SO}_3$ dissolved in the sulfuric acid determines the strength of the oleum. In simple words when sulphur trioxide ${SO}_3$ is reacted with concentrated sulphuric acid $H_2{SO}_4$a yellowish and oily substance is produced, this substance is known as oleum $H_2{S}_2{O}_7$.

$H_2{SO}_4+{SO}_3⟶H_2{S}_2{O}_7$

Oleum is a widely used industrial chemical utilized as an intermediate to produce many different organic and inorganic chemicals.
These include sulfonation (chemically adding sulfate) processes, nylon manufacturing, the production of dyes, nitrating reactions and hydrofluoric acid (HF) production.
Generally when released into the upper atmosphere, oleum exists as sulfuric acid particles or droplets. The acid particles dissolve in clouds, which results in the formation of fog, rain, or snow, resulting in very dilute acid solutions.
Therefore, the molecular formula of Oleum is $H_2{S}_2{O}_7$. Hence option C is the required answer.

Note:
You should know that Oleum is dangerous to human health. Oleum is rapidly destructive to all body tissues, causing severe burns which may result in scarring. So handle with care!