Which one of the following order represents the correct sequence of the increasing basic nature of the given oxides?

The basic (metallic) character of an oxide depends on the metallic character of the element producing that oxide.
• Moving across a period from left to right, metallic character decreases, so basic strength of the oxides decreases and acidic strength increases.
• Moving down a group, metallic character increases, so the oxides become more basic.

Let us analyse each oxide in the list.

1. $$\text{Al}_2\text{O}_3$$ is formed by aluminium, a borderline element situated just after the strictly metallic elements of Period 3. Its oxide is amphoteric (shows both acidic and basic behaviour) and therefore has the least basic character among the four oxides given.

2. $$\text{MgO}$$ is formed by magnesium, a Group 2 element (alkaline-earth metal) in Period 3. Group 2 oxides are basic but noticeably less basic than the oxides of Group 1 (alkali metals) in the same period.

3. $$\text{Na}_2\text{O}$$ is the oxide of sodium, a Group 1 element in Period 3. The oxides of alkali metals are strongly basic.

4. $$\text{K}_2\text{O}$$ is the oxide of potassium, the next member of the same Group 1 (alkali metals). Because metallic character increases down the group, $$\text{K}_2\text{O}$$ is even more basic than $$\text{Na}_2\text{O}$$.

Putting these observations together, the correct ascending order of basic strength is
$$\text{Al}_2\text{O}_3 \lt \text{MgO} \lt \text{Na}_2\text{O} \lt \text{K}_2\text{O}$$

This sequence matches Option D.

Final Answer: Option D which is: $$\text{Al}_2\text{O}_3 \lt \text{MgO} \lt \text{Na}_2\text{O} \lt \text{K}_2\text{O}$$