Question

Assertion: Both ${H_2}{S_2}{O_2}$ and ${H_2}{S_2}{O_3}$ contain $S = S$ bonds.
Reason: ‘ic’ acids are more acidic than ‘ous’ acids.
A.Both assertion and reason are true and reason is the correct explanation of assertion.
B.Both assertion and reason are correct and reason is not the correct explanation of assertion
C.Assertion is true but reason is false
D.Assertion is false but reason is true

Answer 1

Hint: To answer this question, you must recall the structure of the oxoacids of Sulphur. As the name suggests, an oxo acid consists of oxygen atoms. Thus, the oxo acids of Sulphur are acids containing Sulphur and oxygen.

Complete step by step answer:
Sulphur atom has six valence electrons in its valence shell and also has vacant d orbitals in its valence shell. Thus, it can share six electrons.
${H_2}{S_2}{O_2}$ is known as dihydroxy disulfide or hypo dithionous acid. It is the reduced form of an oxoacid of Sulphur and Sulphur is in the $ + 1$ oxidation state. Though there are no $S = S$ double bonds in its primary structure, its isomeric forms have a Sulphur-Sulphur double bond. It is the equivalent acid or the hydrated form of disulfur monoxide. It exists in equilibrium with another Sulphur oxoacid with the same formula known as thiosulfurous acid.
${H_2}{S_2}{O_3}$ is known as thiosulphuric acid. It is an oxoacid of Sulphur with Sulphur in the oxidation state of $ + 4$. It can be prepared by the acidification of the aqueous solutions of thiosulfate salts. The acid decomposes readily in water and forms a variety of decomposition products including Sulphur, Sulphur dioxide, sulphuric acid, hydrogen sulphide and polythionates. The central Sulphur atom forms an $S = S$ double bond with the terminal Sulphur atom. Thus, the assertion is correct.
‘ic’ acids have an extra hydrogen atom present than the ‘ous’ acids. Due to the presence of more oxygen atoms, the oxidation number of the central atom is higher thus increasing the acidic strength of the acid.
Thus, the reason is also true but does not give an explanation for the assertion.

Hence, the correct option is B.

Note:
${H_2}{S_2}{O_2}$ is known as thiosulfurous acid. It is a hypothetical compound. It has a lower oxidation state of Sulphur than other oxoacids. The oxidation state is $ + 1$. It can also be said as the equivalent acid of Sulphur suboxide or disulfur monoxide.