Name the ion that is responsible for the blue colour of an aqueous solution of a salt.

Give a chemical test to distinguish between the calcium nitrate solution and zinc nitrate solution.

A metal which is used in the rechargeable battery, was added to sodium hydroxide solution, a colourless gas was evolved and after the complete reaction the solution was colourless.

Name the metal added to sodium hydroxide solution.

Write the equation for the reaction of $\mathrm{Zn}$ metal/zinc salt solution with ammonium hydroxide.

Write the equation for the reaction of $\mathrm{Zn}$ metal/zinc salt solution with sodium hydroxide and ${\mathrm{H}}_2$ gas is evolved.

Name the compound in which the solution becomes a deep/inky blue colour when excess of ammonium hydroxide is added to it