Answer: They have low ionisation enthalpies and lose the single ns1 electron easily.
- A They have low ionisation enthalpies and lose the single ns1 electron easily
- B They have the highest ionisation enthalpies and hold the ns1 electron very tightly
- C They have completely filled d-orbitals
- D They gain an electron to form stable anions
Correct answer: A. They have low ionisation enthalpies and lose the single ns1 electron easily
Explanation: Alkali metals have the lowest ionisation enthalpies in their periods, so they readily lose the loosely held ns1 electron, making them the most electropositive (strongly metallic) elements.
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.