Group 2 solubility trends increase for hydroxides down the group

Steps:

• Recall that down Group 2, cation size increases from Ca²⁺ to Ba²⁺, reducing charge density.
• For hydroxides, this causes solubility to increase as lattice energy decreases more than hydration energy.
• Compare to other properties: carbonate stability rises, sulfate solubility falls, and reaction rate per gram drops due to higher atomic mass.
• Confirm B matches the increasing trend from Ca(OH)₂ (sparingly soluble) to Ba(OH)₂ (more soluble).

Why B is correct:

• Solubility of Group 2 hydroxides increases down the group per the trend where larger cations lower the energy difference between lattice and hydration enthalpies, favoring dissolution.

Why the others are wrong:

• A: Ease of carbonate decomposition decreases as thermal stability increases with cation size.
• C: Solubility of sulfates decreases down the group due to reduced hydration energy outweighing lattice energy drop.
• D: Volume of hydrogen per gram decreases because heavier Ba produces fewer moles per gram despite similar reactivity.

Final answer: B