What is the molecular formula of Marshall's acid?
\[
  A.{\text{ }}{H_2}S{O_5} \\
  B.{\text{ }}{H_2}{S_2}{O_8} \\
  C.{\text{ }}{H_2}S{O_4} \\
  D.{\text{ }}{H_2}{S_2}{O_7} \\
 \]

Hint- In order to find the molecular formula, first we have to understand what Marshall's acid basically is. Then we will proceed further by making its structure.

Complete answer:
Peroxydisulfuric Acid is a colorless solid and also called Marshall’s acid, and one of the most powerful peroxyacid oxidants available. Peroxydisulfuric Acid is an inorganic compound with the chemical formula \[{H_2}{S_2}{O_8}\] . It can be generated from potassium or ammonium persulfate in an acidic solution. It is an anhydride of sulfuric and peroxydisulfuric acid and may be prepared by oxidation of oleum with ozone or hydrogen peroxide. peroxydisulfuric acid can be produced by electrolyzing an aqueous solution containing sulfate ions in an electrolysis reactor should be produced by electrolyzing.
In structural terms it can be written \[H{O_3}SOOS{O_3}H\] . It contains sulfur in its +6 oxidation state, but it also contains a peroxide group, which is why it appears to be in a higher oxidation state than sulfates. Its salts, commonly known as persulfates, are industrially important but the acid itself is not. The salts contain the peroxydisulfate ion. They are powerful oxidizing agents.
Structure:

Hence, the correct answer is \[{H_2}{S_2}{O_8}\]

So, option B is the correct option.

Note- Peroxydisulfuric acid is the inorganic compound with the chemical formula \[{H_2}{S_2}{O_8}\] . Also called Marshall's acid after its inventor Professor Hugh Marshall. The acid is prepared by the reaction of chlorosulphuric acid with hydrogen peroxide. Another method is the electrolysis of moderately concentrated sulfuric acid (60-70%) with platinum electrodes at high current density and voltage.