Please clarify this doubt.If lattice energy decreases as one moves from Mg(OH)2 to Ba(OH)2, then why thermal stabilityincreases as we move from Mg(OH)2 to Ba(OH)2 ???Please explain me without missing out any minute details.

Lattice energy is the amount of energy required to bring a cation and an anion from infinitely long distance to form an ionic bond. Here Ba is more electropositive than Mg. Therefore energy required is less for an ionic bonding hence making the bond more stabler as it is stronger compared to bond formation between Mg and hydroxyl ion.