Final answer:
The thermal stability of Group 2 hydroxides increases down the group due to increasing ionic size leading to decreased lattice energies, which correlates with increased stability.
Step-by-step explanation:
The thermal stability of Group 2 hydroxides increases down the group due to increasing ionic size. This is because as you move down the group in the periodic table, the ionic radius increases, which in turn decreases the lattice energy of the compound. The solid consists of divalent ions and has much higher lattice energies than solids with monovalent ions. Additionally, since the lattice energy is inversely related to the size of the ions, an increase in ionic size means that the lattice energy will decrease, which results in increased thermal stability. Therefore, higher thermal stability correlates with a decrease in lattice energy due to the increase in ionic size.