Which of the following oxides when dissolved in water gives a solution which turns blue litmus red?

Options

A. `MgO`
B. `CaO`
C. `CO_2`
D. `CuO`

Explanation

To determine which oxide, when dissolved in water, gives a solution that turns blue litmus red, we can follow these steps:

### Step 1: Understand the nature of oxides
- Oxides can be classified into two categories: metallic oxides and non-metallic oxides.
- Metallic oxides are generally basic in nature, while non-metallic oxides are acidic in nature.

### Step 2: Identify the options
- We need to analyze the given oxides to determine whether they are metallic or non-metallic. The options typically include:
1. MgO (Magnesium oxide)
2. CaO (Calcium oxide)
3. CO2 (Carbon dioxide)
4. CuO (Copper oxide)

### Step 3: Classify the oxides
- **MgO**: Magnesium is a metal, so MgO is a metallic oxide (basic).
- **CaO**: Calcium is also a metal, making CaO a metallic oxide (basic).
- **CO2**: Carbon is a non-metal, so CO2 is a non-metallic oxide (acidic).
- **CuO**: Copper is a metal, so CuO is a metallic oxide (basic).

### Step 4: Determine the effect on litmus
- A solution that is acidic will turn blue litmus paper red.
- Since CO2 is the only non-metallic oxide in the options, it will produce an acidic solution when dissolved in water.

### Step 5: Conclusion
- The oxide that, when dissolved in water, gives a solution that turns blue litmus red is **CO2 (Carbon dioxide)**.

### Final Answer
- The correct answer is **CO2 (Carbon dioxide)**.

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