JEE Advanced 2018 Paper 1 Chemistry: Paragraph 1

A pale green crystalline salt X (molar mass $278\ \mathrm{g\,mol^{-1}}$, a heptahydrate) dissolves in water to give a pale green solution. This solution gives a deep blue precipitate with $\mathrm{K_3[Fe(CN)_6]}$, a white precipitate with $\mathrm{BaCl_2}$ that is insoluble in dilute HCl, and it decolourises acidified $\mathrm{KMnO_4}$. On strong heating, X first loses its water of crystallisation and then decomposes to give a brown-red solid residue Y and a gaseous mixture Z of two oxides of sulphur in equal mole ratio. Z is passed through aqueous $\mathrm{BaCl_2}$ solution and gives a white precipitate. Take atomic masses Fe = 55.8, S = 32.0, O = 16.0, Ba = 137.3, H = 1.0.