Answer: Decreases.
- A Increases steadily
- B Decreases
- C Remains constant
- D First increases then decreases
Correct answer: B. Decreases
Explanation: Down the group atomic size increases and the outer electron is more shielded and farther from the nucleus, so ionisation enthalpy decreases from Li to Cs.
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.