Which one of the following orders presents the correct sequence of the increasing basic nature of the given oxides? (1) K2O

While moving from left to right in periodic table basic character of oxide of elements will decrease.

   $\therefore \to Increa\sin g basic strengthAl2O3<MgO<Na2O$ 

and while descending in the group basic character of corresponding oxides increases. 

  $\therefore \to Increa\sin g basic strengthNa2O<K2O$

$\therefore Correct Order is Al2O3 < MgO <Na2O <K2O$