Mg(OH)2<Sr(OH)2<Ca(OH)2<Ba(OH)2
Ba(OH)2<Sr(OH)2<Ca(OH)2<Mg(OH)2
Ba(OH)2<Ca(OH)2<Sr(OH)2<Mg(OH)2
Mg(OH)2<Ca(OH)2<Sr(OH)2<Ba(OH)2
The correct order of thermal stability of hydroxide is Mg(OH)2<Ca(OH)2<Sr(OH)2<Ba(OH)2. On moving down the group, the lattice enthalpy increases and the thermal stability increases. Hence, option D is correct.