Passing H₂S gas into a mixture of Mn²⁺, Ni²⁺, Cu²⁺ and Hg²⁺ ions in an acidified aqueous solution precipitates

Amongst the compounds given, the one that would from a brilliant coloured dye on treatment with NaNO₂ in dil. HCl followed by addition to an alkaline solution of $$\beta$$-naphthlol is

The following carbohydrate is

The equilibrium

$$2C{u^+} \to Cu^\circ + C{u^{2+}}$$

In aqueous medium at 25$$^\circ$$C shifts towards the left in the presence of