When XO₂ is fused with an alkali metal hydroxide in presence of an oxidizing agent such as KNO₃ ; a dark green product is formed which disproportioates in acidic solution to afforda dark purple solution. X is :

Which of the following ions does not liberate hydrogen gas on reaction with dilute acids ?

The pair of compounds having metals in their highest oxidation state is :

In the following reactions, ZnO is respectively acting as a/an :

(a) ZnO + Na₂O $$\to$$ Na₂ZnO₂

(b) ZnO + CO₂ $$\to$$ ZnCO₃