Question

The metal oxides which cannot be reduced by CO are: \[ \text{I. }Li_2O \] \[ \text{II. }MgO \] \[ \text{III. }Al_2O_3 \] \[ \text{IV. }ZnO \] The correct answer is (only):

• A. II, III, IV only
• B. I, III, IV only
• C. I, II, III only
• D. II, III only

Hint:

Very stable oxides such as \(Li_2O\), \(MgO\), and \(Al_2O_3\) cannot be reduced by carbon monoxide. Zinc oxide is readily reduced by CO during extraction.

Answer 1

The Correct Option is C

Concept: Whether carbon monoxide can reduce a metal oxide is determined using the Ellingham diagram. Metal oxides that are very stable cannot be reduced by CO.

Step 1: Analyze \(Li_2O\). Lithium has very high affinity for oxygen. \[ Li_2O \] is extremely stable. CO cannot reduce it.

Step 2: Analyze \(MgO\). Magnesium oxide is also highly stable. \[ MgO \] cannot be reduced by CO.

Step 3: Analyze \(Al_2O_3\). Aluminium oxide is one of the most stable metal oxides. It is reduced only by electrolytic methods. Therefore CO cannot reduce it.

Step 4: Analyze \(ZnO\). Zinc oxide lies below the CO/CO\(_2\) line in the Ellingham diagram at extraction temperatures. Therefore, \[ ZnO \] can be reduced by CO. Hence it is not included. Therefore the correct set is \[ Li_2O,\;MgO,\;Al_2O_3 \] or \[ \boxed{\text{I, II and III only}} \]