Answer: NaOH and H 2 O 2 (2Na 2 O 2 + 2H 2 O → 4NaOH + O 2 ).
- A NaOH and H<sub>2</sub>O<sub>2</sub> (2Na<sub>2</sub>O<sub>2</sub> + 2H<sub>2</sub>O → 4NaOH + O<sub>2</sub>)
- B Na<sub>2</sub>O and oxygen gas released without any hydroxide formed
- C NaOH alone, with no oxygen or peroxide byproduct at all
- D Na<sub>2</sub>CO<sub>3</sub> and hydrogen peroxide formed via carbonation
Correct answer: A. NaOH and H<sub>2</sub>O<sub>2</sub> (2Na<sub>2</sub>O<sub>2</sub> + 2H<sub>2</sub>O → 4NaOH + O<sub>2</sub>)
Explanation: Na<sub>2</sub>O<sub>2</sub> (sodium peroxide) reacts with water: 2Na<sub>2</sub>O<sub>2</sub> + 2H<sub>2</sub>O → 4NaOH + O<sub>2</sub>. It is used in submarines as an O<sub>2</sub> source.
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.