Which one of the following ordered presents the correct sequence of the increasing basic nature of the given oxides ?
As metallic character of element attached to oxygen atom increases, the difference between the electronegativity values of element and oxygen increases and thus basic character of oxides increases and vice-versa. Hence the increasing correct order of basic nature is Al2O3 < MgO < Na2O < K2O.
The basic nature of oxides depends on the metallic character of their constituent elements. Oxides of metals are basic, and their basic strength increases with increasing metallic character (or decreasing electronegativity) of the metal. Across a period, metallic character decreases from left to right, and down a group, it increases.
Step 1: Identify the positions of the metals in the periodic table:
Step 2: Compare metallic character:
Within Group 1: K (period 4) is more metallic than Na (period 3), so K2O is more basic than Na2O.
Comparing groups: Group 1 metals (Na, K) are more metallic than Group 2 (Mg), which is more metallic than Group 13 (Al). So basic nature order: Al2O3 (amphoteric) < MgO (weak base) < Na2O < K2O (strong bases).
Step 3: Evaluate the options:
Option 1: Al2O3 < MgO < Na2O < K2O matches our reasoning.
Other options are incorrect due to wrong sequences.
Final Answer: The correct sequence is Al2O3 < MgO < Na2O < K2O
Basic nature ∝ Metallic character
Metallic character decreases across a period and increases down a group.
Electronegativity trend: Increases across a period, decreases down a group.
Oxides of highly electropositive metals (e.g., Group 1 and 2) are basic; oxides of less electropositive metals (e.g., Al) are amphoteric.