Answer: Be and Mg among Group 2; none of Group 1.
- A Be and Mg among Group 2; none of Group 1
- B Be and Mg among Group 2; Li among Group 1
- C Ca and Na
- D Sr and K
Correct answer: A. Be and Mg among Group 2; none of Group 1
Explanation: Beryllium and magnesium have electrons too tightly bound to be excited by a flame, so they give no colour; all the alkali metals, including Li, do impart flame colours.
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.