Answer: Increases down the group (larger cations have lower charge density, stabilise CO 3 2- more).
- A Increases down the group (larger cations have lower charge density, stabilise CO<sub>3</sub><sup>2-</sup> more)
- B Decreases steadily down the group as the cation's charge density falls in routine practice
- C Remains essentially identical across most Group 2 carbonate salt overall in most cases
- D Depends mainly on the external storage temperature, not on cation size under typical conditions
Correct answer: A. Increases down the group (larger cations have lower charge density, stabilise CO<sub>3</sub><sup>2-</sup> more)
Explanation: Larger alkaline earth cations (Ca, Sr, Ba) have lower polarising power and stabilise the CO<sub>3</sub><sup>2-</sup> lattice better; BaCO<sub>3</sub> decomposes at the highest temperature.
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.