Sulfur trioxide (alternative spelling sulphur trioxide, also known as nisso sulfan) is the chemical compound with the formula SO3. It has been described as "unquestionably the most [economically] important sulfur oxide". It is prepared on an industrial scale as a precursor to sulfuric acid.
An ampoule of sulfur trioxide
Sulfuric acid or sulphuric acid, known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, and hydrogen, with the molecular formula H2SO4. It is a colorless, odorless, and viscous liquid that is miscible with water.
Sulfuric acid
Drops of concentrated sulfuric acid rapidly decompose a piece of cotton towel by dehydration.
Rio Tinto with its highly acidic water
Domestic acidic drain cleaners usually contain sulfuric acid at a high concentration which turns a piece of pH paper red and chars it instantly, demonstrating both the strong acidic nature and dehydrating property.