Identify the following:
`Na_(2)CO_(3) overset(SO_(2))(rarr) A overset(Na_(2)CO_(2))(rarr) B overset("element S")(rarr)Coverset(I_(2))(rarr)D`
Also mention the oxidation state of `S` in all the compounds

Explanation

`A=NaHSO_(3), B=Na_(2)SO_(3), C=Na_(2)S_(2)O_(3), D=Na_(2)S_(4)O_(6)`