Alkaline earth metals burn in oxygen to form monoxides which are basic in nature (except BeO) and react with water to form sparingly soluble hydroxides. The solubility, thermal stability and the basic character of these hydroxides increase with increasing atomic number from Mg(OH)₂ to Ba(OH)₂. Ionization enthalpy increases from Mg to Ba, hence the M—O bond becomes weaker from Mg to Ba, and hence Mg will form the weakest base. Hence, Mg(OH)₂ is the least basic in nature. The correct option is (i).