The Carius method is a technique used for the quantitative analysis of sulfur. This method involves the oxidation of sulfur to produce sulfuric acid, which is then reacted with barium chloride (BaCl\(_2\)) to form barium sulfate (BaSO\(_4\)), a white precipitate.
Among the options, methionine is the only compound containing sulfur that can react with sodium peroxide to form sulfuric acid.
Chloroxyleneol does not contain sulfur.
Nucleotides and cytosine do not contain sulfur in a form that is detectable by this method.
Therefore, the correct compound 'X' is Methionine.