Answer: Historical preparation of H 2 O 2 : BaO 2 + H 2 SO 4 → BaSO 4 + H 2 O 2.
- A Historical preparation of H<sub>2</sub>O<sub>2</sub>: BaO<sub>2</sub> + H<sub>2</sub>SO<sub>4</sub> → BaSO<sub>4</sub> + H<sub>2</sub>O<sub>2</sub>
- B The electrolytic production of elemental barium metal
- C The direct chemical reduction of barium sulfate to barium sulfide
- D The industrial Solvay process for manufacturing sodium carbonate
Correct answer: A. Historical preparation of H<sub>2</sub>O<sub>2</sub>: BaO<sub>2</sub> + H<sub>2</sub>SO<sub>4</sub> → BaSO<sub>4</sub> + H<sub>2</sub>O<sub>2</sub>
Explanation: Before modern methods, H<sub>2</sub>O<sub>2</sub> was made by treating BaO<sub>2</sub> with cold dilute H<sub>2</sub>SO<sub>4</sub>, giving insoluble BaSO<sub>4</sub> precipitate and H<sub>2</sub>O<sub>2</sub> solution.
Each s-block metal ion emits a characteristic flame colour because heating excites electrons to higher energy levels; light is emitted as they fall back, with the colour determined by the specific energy gap.
Concept context
Group 1 (alkali metals) and Group 2 (alkaline earth metals). Learn their reactions with water and air, important compounds like NaOH, Na₂CO₃, and CaCO₃, and anomalous behaviour of lithium and beryllium.