Reactivity and stability trends in Group 2 elements

Steps:

• Recall that reactivity of Group 2 metals increases down the group due to decreasing ionization energy.
• Barium, below calcium, is more reactive than calcium.
• Thermal stability of Group 2 carbonates increases down the group as larger cations polarize the carbonate ion less, stabilizing it.
• Barium carbonate is more stable than calcium carbonate.

Why B is correct:

• Matches the trend: barium's higher reactivity and barium carbonate's greater stability follow the group 2 periodicity law.

Why the others are wrong:

• A: Incorrectly states calcium carbonate is more stable, opposite of the stability trend.
• C: Wrong on reactivity; calcium is less reactive than barium.
• D: Errors on both; calcium is less reactive, and its carbonate is less stable.

Not enough information on the table to confirm phrasing, but based on chemistry, B fits.

Final answer: B