Question

Which of the following is a basic oxide? ________.

• A. CrO
• B. $CrO_{3}$
• C. $Mn_{2}O_{7}$
• D. $Cr_{2}O_{3}$
• E. $V_{2}O_{5}$

Hint:

Basicity $\propto \frac{1}{\text{Oxidation State}}$.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept
The acid-base character of a metal oxide is strongly correlated with the oxidation state of the metal. As the oxidation state of a metal increases, the covalent character of the metal-oxygen bond increases, which in turn increases the acidic character of the oxide.
Step 2: Key Formula or Approach
The general trend for transition metal oxides is:
- Low oxidation state: The oxide is basic. - Intermediate oxidation state: The oxide is amphoteric. - High oxidation state: The oxide is acidic.
Step 3: Detailed Explanation
Let's determine the oxidation state of the metal in each oxide, assuming oxygen has an oxidation state of -2.
(A) CrO: The oxidation state of Cr is +2. This is a low oxidation state for chromium, so CrO is a basic oxide.
(B) CrO\(_3\): The oxidation state of Cr is +6. This is a high oxidation state, so CrO\(_3\) is an acidic oxide. (It is the anhydride of chromic acid, H\(_2\)CrO\(_4\)).
(C) Mn\(_2\)O\(_7\): The oxidation state of Mn is +7. This is the highest oxidation state for manganese, so Mn\(_2\)O\(_7\) is a strongly acidic oxide. (It is the anhydride of permanganic acid, HMnO\(_4\)).
(D) Cr\(_2\)O\(_3\): The oxidation state of Cr is +3. This is an intermediate oxidation state for chromium, so Cr\(_2\)O\(_3\) is an amphoteric oxide.
(E) V\(_2\)O\(_5\): The oxidation state of V is +5. This is the highest oxidation state for vanadium. V\(_2\)O\(_5\) is amphoteric with predominantly acidic character.
Based on this trend, the oxide with the metal in the lowest oxidation state, CrO, is the basic oxide.
Step 4: Final Answer
The basic oxide is CrO.