Which is the most basic oxide? A) \[BeO\] B) \[CaO\] C) \[MgO\] D) \[BaO\]
Hint: All the oxides given in the option are made up of group 2 elements i.e. alkaline earth metals. The order of basicity depends upon the atomic size. Before answering this question you must know the trend of elements and where they are placed and what their atomic number is then it is easy to answer this question.
Complete answer: Firstly we look at the trend of atomic size for this element. Elements are placed in this way in group 2. On moving down the group atomic size increases. Beryllium will have the smaller atomic radii whereas barium will have the larger atomic radii. \[Be\] \[Mg\] \[Ca\] $Sr$ \[Ba\] As the atomic radius increases, reactivity also increases due to which the basic character of oxides also increases. Option A) this is an incorrect option as Beryllium has atomic radius smaller as compared to other elements since it has atomic number 4. Since atomic radius is smaller, the oxide i.e. \[BeO\]will be the least basic. Option B) this is an incorrect option as Calcium has atomic radius lower than barium thus it will have basic order lower than barium. Thus \[CaO\] is not the one which is the most basic oxide. Option C) this is an incorrect option as Magnesium has atomic radius even lower than Calcium so it will have the lowest basicity. Option D) this is a correct option as barium has larger atomic radius out of all the elements given therefore it will have the most basic oxide as higher atomic radius will lead to more reactivity and thus the order of basicity increases. Therefore \[BaO\] is the most basic oxide.
Note: We need to remember that on moving down the group, atomic size increases due to which reactivity increases which will lead to the increase in basicity. Barium has higher atomic size or radius due to which it has highest reactivity and thus the basic order increases. Therefore \[BaO\] is the most basic oxide.