State one relevant observation for each of the following reactions:

(i) Action of concentrated nitric acid on copper.

(ii) Addition of excess ammonium hydroxide into copper sulphate solution.

(iii) A piece of sodium metal is put into ethanol at room temperature.

(iv) Zinc carbonate is heated strongly.

(v) Sulphide ore is added to a tank containing oil and water, and then stirred or agitated with air.

(i) Reddish brown fumes of nitrogen dioxide gas are liberated when copper reacts with conc. nitric acid.

(ii) Deep blue or inky blue solution is formed when excess of ammonium hydroxide is added to copper sulphate solution.

(iii) Effervescence of a gas is seen when a piece of sodium metal is put into ethanol at room temperature. The gas extinguishes a burning splint with a pop sound which confirms that the gas is hydrogen.

(iv) A residue which is yellow when hot and white when cold is formed.

(v) The ore is wetted by the oil and gets separated from the gangue in the form of froth. The impurities gets wetted by water and remain behind in the sink. Since the ore is lighter, it comes on the surface with the froth and impurities are left behind.