When a black powder 'X' is heated with an alkali metal bromide and concentrated H ₂ SO ₄ , it yields a transition metal sulphate, an alkali metal sulphate, water, and a reddish-brown gas 'Z'. Identify 'X' and 'Z'.

Step-by-step solution

The reaction of an alkali metal bromide (such as NaBr ) with concentrated H ₂ SO ₄ and manganese dioxide ( MnO ₂ ) produces bromine gas ( Br ₂ ). The chemical equation is: 2 NaBr + MnO ₂ + 2 H ₂ SO ₄ Na ₂ SO ₄ + MnSO ₄ + 2 H ₂ O + Br ₂ In this reaction, MnO ₂ is a black powder (X) that acts as an oxidising agent, oxidising bromide ions to bromine gas ( Br ₂ ), which is a reddish-brown gas (Z). KMnO ₄ is dark purple, not a black powder. CuO does not oxidise bromides in this manner. NO ₂ is reddish-brown but is evolv