2019 H2 Chem P1 Q10 — Group 2 Solution

The answer is D.

Group 2 metals react by losing their two valence electrons to form \(\text{M}^{2+}\) ions, so reactivity rises as the valence electrons become easier to remove.
• D: down the group the number of electron shells increases, so the valence electrons are further from the nucleus and more shielded by inner electrons. The nucleus attracts them less strongly, less energy is needed to remove them, and the metal reacts more readily.

• A: electron affinity is about gaining an electron. Group 2 metals react by losing electrons, and a greater tendency to gain electrons would not make losing them easier.
• B: electronegativity decreases down Group 2, and an increase would make electrons harder to lose, not easier.
• C: nuclear charge does increase down the group, but on its own it would hold the valence electrons more tightly. Its effect is outweighed by the extra shells (greater distance and shielding), so it does not explain the rise in reactivity.