(viii) Amongest the following groups of oxides, the group containing oxides that cannot be reducing by carbon to give the respective metals is.

Options

A. `Cu_(2) O,SnO_(2)`
B. `Fe_(2) O_(3),ZnO`
C. `CaO,K_(2)O`
D. `PbO,Fe_(3) O_(4)`

Explanation

To solve the question of which group of oxides cannot be reduced by carbon to give the respective metals, we need to analyze the reactivity of the metals involved and their oxides. Here’s a step-by-step breakdown:

### Step 1: Understand the concept of reduction
Reduction is a chemical process where a substance gains electrons or decreases its oxidation state. In the context of metal oxides, reduction typically involves converting the metal oxide back to the metal, often using a reducing agent like carbon.

### Step 2: Identify the metals in the given oxides
The question mentions oxides of sodium, potassium, magnesium, and calcium. We need to consider the reactivity of these metals:
- Sodium (Na)
- Potassium (K)
- Magnesium (Mg)
- Calcium (Ca)

### Step 3: Determine the reactivity of the metals
These metals are known for their reactivity:
- Sodium and potassium are alkali metals and are highly reactive.
- Magnesium and calcium are alkaline earth metals and are also quite reactive, though less so than sodium and potassium.

### Step 4: Analyze the ability of carbon to reduce these oxides
Carbon can reduce metal oxides to metals, but this is not true for all metals:
- Highly reactive metals (like sodium and potassium) have a strong affinity for oxygen and cannot be reduced by carbon because they will react with carbon instead.
- Magnesium and calcium, while less reactive than sodium and potassium, still have a significant affinity for oxygen and can also resist reduction by carbon.

### Step 5: Conclusion
Based on the analysis, the group of oxides that cannot be reduced by carbon to give the respective metals includes:
- Sodium oxide (Na2O)
- Potassium oxide (K2O)
- Magnesium oxide (MgO)
- Calcium oxide (CaO)

Thus, the answer is that the group containing oxides that cannot be reduced by carbon includes calcium oxide and potassium oxide.

### Final Answer:
The group containing oxides that cannot be reduced by carbon to give the respective metals is the group of calcium oxide and potassium oxide.

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