Which oxide is more basic, `MgO` or `BaO`? Whay?

Explanation

BaO, because basic character of oxides increases down the group. On going down the group, the size of the cation increases and hence its acidic nature becomes less. As a result those with smaller sizes generally become amphoteric or more acidic. MgO is a basic oxide too but BaO with a larger sized `Ba^(+2)` ion has greater basic nature. This can also be proven by looking at the strength of the hydroxide bases. Where `Ba(OH)_2` is a strong base, `Mg(OH)_2` is a weak base and poorly soluble in water also.