Answer: Acetylene (C 2 H 2 ) and Ca(OH) 2.
- A Acetylene (C<sub>2</sub>H<sub>2</sub>) and Ca(OH)<sub>2</sub>
- B Ethylene and CaO in general practice
- C CO<sub>2</sub> and Ca(OH)<sub>2</sub> as frequently described
- D CO and CaCO<sub>3</sub> in most textbook accounts
Correct answer: A. Acetylene (C<sub>2</sub>H<sub>2</sub>) and Ca(OH)<sub>2</sub>
Explanation: CaC<sub>2</sub> + 2H<sub>2</sub>O → Ca(OH)<sub>2</sub> + C<sub>2</sub>H<sub>2</sub>. This reaction was historically used to generate acetylene for lamps (carbide lamps).
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.