Which of the following oxides is least basic in nature?

Explanation:

The basicity of metal oxides generally increases as we move down a group in the periodic table. This trend is due to the increasing size of the metal cations, which leads to weaker electrostatic attraction between the cation and the oxide ion, facilitating the release of hydroxide ions in solution. Consequently, the oxides of heavier alkaline earth metals like barium (BaO) are more basic than those of lighter metals like beryllium (BeO).

Therefore, the order of basicity from least to most basic is:

BeO < MgO < CaO < BaO