Question

Which is more basic $A{l_2}{O_3}$or$MgO$?

Answer 1

Keep in mind the periodic table while answering this question. Mg belongs to the s block whereas Al belongs to the p block. Thus we can say that Mg is left to Al in terms of a period.
Also consider that $A{l_2}{O_3}$ is an amphoteric oxide. Metal oxides which react with both acids as well as bases to produce salts and water are known as amphoteric oxides. As a rule all the metal oxides will be basic and all the non-metal oxides are acidic.

Complete answer:
There are many things that point out to the fact that $MgO$ is more basic than $A{l_2}{O_3}$.
We observe that metals are mostly present on the left side of the periodic table and nonmetals towards the right side of a period. Since the oxides of non-metals are acidic and that of metals are basic we say that along a period from left to right basic character decreases.
Observing the periodic table and the positions of Mg and Al we can conclude that $MgO$is more basic than $A{l_2}{O_3}$.
Another point that confirms the answer is that $A{l_2}{O_3}$ is an amphoteric oxide whereas $MgO$ is a basic metal oxide. Which gives us more confirmation that $MgO$ is more basic than$A{l_2}{O_3}$

Note:

${K_2}O$	$MgO$	$A{l_2}{O_3}$	$Si{O_2}$	$C{O_2}$
Strongly Basic	Basic	Amphoteric	Weakly Acidic	Acidic

Also as we go down a group the basicity of oxides increases with increases. For example in group V, $N{O_2}$and ${P_4}{O_8}$ are acidic, $A{s_2}{O_4}$and $S{b_2}{O_3}$ are amphoteric, $B{i_2}{O_3}$ is basic.
Even when we consider the oxides of the second group elements basicity increase in the following order
$BeO{\text{ }} < {\text{ }}MgO{\text{ }} < {\text{ }}CaO{\text{ }} < {\text{ }}SrO{\text{ }} < {\text{ }}BaO$