The order of basic strength of given oxide:

The metallic character is scaled to the basic character. Therefore, as you move from left to right on the periodic table, it grows smaller.
Comparing the d-block metal oxides to the s-block and p-block metal oxides, they are less basic.

$\mathrm{MGO}\to \mathrm{Group} 2$

${\mathrm{Al}}_2{\mathrm{O}}_3 \to \mathrm{Group} 13$

${\mathrm{Na}}_2\mathrm{O}\to \mathrm{Group} 1$

$\mathrm{CuO}\to \mathrm{d}-\mathrm{block}$

The basicity will be arranged in the following order:${\mathrm{Na}}_2\mathrm{O}>\mathrm{MgO}>{\mathrm{Al}}_2{\mathrm{O}}_3>\mathrm{CuO}.$