An aqueous solution of a mixture of two inorganic salts, when treated with dilute HCl, gave a precipitate (P) and a filtrate (Q). The precipitate (P) was found to dissolve in hot water. The filtrate (Q) remained unchanged, when treated with H₂S in a dilute mineral acid medium. However, it gave a precipitate (R) with H₂S in an ammoniacal medium. The precipitate R gave a coloured solution (S), when treated with H₂O₂ in an aqueous NaOH medium.

The coloured solution S contains

P and Q are isomers of dicarboxylic acid C₄H₄O₄. Both decolorise Br₂/H₂O. On heating, P forms the cyclic anhydride. Upon treatment with dilute alkaline KMnO₄, P as well as Q could produce one or more than one from S, T and U.

Compounds formed from P and Q are, respectively,

P and Q are isomers of dicarboxylic acid C₄H₄O₄. Both decolorise Br₂/H₂O. On heating, P forms the cyclic anhydride. Upon treatment with dilute alkaline KMnO₄, P as well as Q could produce one or more than one from S, T and U.

In the following reaction sequences V and W are, respectively,

A fixed mass m of a gas is subjected to transformation of states from K to L to M to N and back to K as shown in the figure.

The succeeding operations that enable this transformation of states are