JEE Advanced 2021 Paper 2 Chemistry: Paragraph 2

A pale-green crystalline solid $\mathrm{X}$ dissolves readily in water. Its aqueous solution gives a deep-blue precipitate with $\mathrm{K_3[Fe(CN)_6]}$, and a white precipitate with $\mathrm{BaCl_2}$ that is insoluble in dilute $\mathrm{HCl}$. On warming with $\mathrm{NaOH}$, $\mathrm{X}$ liberates a gas that turns moist red litmus blue and gives a brown colour with Nessler's reagent. $\mathrm{X}$ is a double salt (Mohr's salt type) of molar mass $392\ \mathrm{g\,mol^{-1}}$ containing six molecules of water of crystallisation. A fresh solution of $\mathrm{X}$ is mixed with a little $\mathrm{NaNO_3}$ solution, and concentrated $\mathrm{H_2SO_4}$ is poured slowly down the side of the test tube, producing a brown ring of the complex $\mathrm{Z}$, written $[\mathrm{Fe(H_2O)_5(NO)}]^{2+}$, in which nitric oxide is bound as $\mathrm{NO^+}$.