Answer: The cation polarises the carbonate ion less, stabilising it.
- A The cation polarises the carbonate ion less, stabilising it
- B The cation becomes smaller and far more strongly polarising
- C Lattice enthalpy increases sharply
- D The carbonate ion becomes more covalent
Correct answer: A. The cation polarises the carbonate ion less, stabilising it
Explanation: Larger cations down the group have lower polarising power and distort the CO<sub>3</sub><sup>2-</sup> ion less, so the carbonates need higher temperatures to decompose and are thermally more stable.
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.