Question

Which of the following oxides is highly basic?

• A. \( \text{Cr}_2\text{O}_3 \)
• B. \( \text{Al}_2\text{O}_3 \)
• C. \( \text{MgO} \)
• D. \( \text{Na}_2\text{O} \)

Hint:

The basic character of metal oxides increases as the electropositivity of the metal increases. Alkali metal oxides are generally highly basic, alkaline earth metal oxides are basic, and oxides of metalloids and non-metals are acidic or amphoteric. Consider the position of the metal in the periodic table to predict the basicity of its oxide.

Answer 1

The Correct Option is D

The basicity of metal oxides depends on the electropositivity of the metal.
More electropositive metals tend to form more basic oxides because the \( M-O \) bond is more ionic, leading to the easy release of \( O^{2-} \) ions (which react with water to form \( OH^- \) ions, increasing basicity).
Let's analyze the given oxides: - \( \text{Na}_2\text{O} \): Sodium (Na) is an alkali metal (Group 1), which are highly electropositive.
Its oxide is expected to be strongly basic.
\( \text{Na}_2\text{O} + \text{H}_2\text{O} \rightarrow 2\text{NaOH} \) (strong base).
- \( \text{MgO} \): Magnesium (Mg) is an alkaline earth metal (Group 2), which is less electropositive than alkali metals.
Its oxide is basic but less so than alkali metal oxides.
\( \text{MgO} + \text{H}_2\text{O} \rightarrow \text{Mg(OH)}_2 \) (weak base).
- \( \text{Al}_2\text{O}_3 \): Aluminum (Al) is a metalloid.
Its oxide is amphoteric, meaning it can react with both acids and bases.
It is not highly basic.
- \( \text{Cr}_2\text{O}_3 \): Chromium (Cr) is a transition metal.
Its oxide is also amphoteric.
It is not highly basic.
Comparing the electropositivity of the metals: Na is the most electropositive among Na, Mg, Al, and Cr.
Therefore, its oxide, \( \text{Na}_2\text{O} \), is expected to be the most basic.
The order of basicity generally follows the order of electropositivity of the metals: \( \text{Na}>\text{Mg}>\text{Al} \approx \text{Cr} \) (in terms of oxide basicity).
Thus, \( \text{Na}_2\text{O} \) is the most basic oxide among the given options.