AIEEE 2011 Solved Paper

You should know that,(1) In a period, from left to right the acidic strength increases that mean basic nature decreases.(2) In a group, from top to bottom the basic nature increases that means acidic nature decreases.$\mathrm{Na}, \mathrm{Mg}, \mathrm{Al}$ and $\mathrm{K}$ are present in periodic table like this :-So, you can see $\mathrm{Na}, \mathrm{Mg}$ and $\mathrm{Al}$ are present in same period so the order of basic nature among $\mathrm{Na}, \mathrm{Mg}$ and $\mathrm{Al}$ is $\mathrm{Na} > \mathrm{Mg} > \mathrm{Al}$.And $\mathrm{Na}$ and $\mathrm{K}$ are from same group so basic nature of $\mathrm{K} > \mathrm{Na}$.So the correct order of oxides$\mathrm{Al}_2\mathrm{O}_3 < \mathrm{MgO} < \mathrm{Na}_2\mathrm{O} < \mathrm{K}_2\mathrm{O}$