2023 H2 Chem P1 Q7 — Group 2 Solution

The answer is A (1 and 2).
• Statement 1, correct. Down Group 2, \(E^{\ominus}(\text{M}^{2+}/\text{M})\) becomes more negative (Data Booklet: Mg -2.38 V, Ca -2.87 V, Sr -2.89 V, Ba -2.90 V), so the metals are more readily oxidised to \(\text{M}^{2+}\) and are stronger reducing agents.
• Statement 2, correct. Down the group the \(\text{M}^{2+}\) ions become larger with the same charge, so their charge density and polarising power decrease. The carbonate ion's electron cloud is distorted less, its C-O bonds are weakened less, and more energy is needed to decompose the carbonate, so thermal stability increases.
• Statement 3, incorrect. The cation's charge stays 2+ while its radius increases, so its charge density decreases.
B and D: both include statement 3, which is wrong.
C: leaves out statement 2, which is also correct.