Answer: One valence electron (ns 1 ).
- A One valence electron (ns<sup>1</sup>)
- B Two valence electrons
- C Full d orbitals
- D Zero valence electrons
Correct answer: A. One valence electron (ns<sup>1</sup>)
Explanation: All alkali metals have one valence electron in the outermost s orbital (ns<sup>1</sup> configuration).
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.