The substance which can turn blue litmus to red is :

Options

A. baking soda
B. milk of magnesia
C. lemon juice
D. calamine solution

Answer

To solve the question "The substance which can turn blue litmus to red is:", we need to identify which substance among the given options is acidic in nature, as only acidic substances can turn blue litmus paper red.

### Step-by-Step Solution:

1. **Understand Litmus Paper**:
- Litmus paper is a natural indicator that changes color based on the acidity or basicity of a solution.
- Blue litmus paper turns red in acidic solutions and red litmus paper turns blue in basic solutions.

2. **Identify the Options**:
- The question provides four options. We need to evaluate each one to determine if it is acidic.

3. **Evaluate Each Option**:
- **Option 1: Baking Soda**:
- Baking soda is sodium bicarbonate (NaHCO₃), which is a basic substance. It will not turn blue litmus red.
- **Option 2: Milk of Magnesia**:
- Milk of magnesia is magnesium hydroxide (Mg(OH)₂), which is also a basic substance. It will not turn blue litmus red.
- **Option 3: Lemon Juice**:
- Lemon juice is acidic due to the presence of citric acid. It will turn blue litmus paper red.
- **Option 4: Calamine Solution**:
- Calamine solution is primarily zinc carbonate (ZnCO₃), which is basic in nature. It will not turn blue litmus red.

4. **Conclusion**:
- Among the options, only lemon juice (Option 3) is acidic and can turn blue litmus paper red. Therefore, the correct answer is lemon juice.

### Final Answer:
The substance which can turn blue litmus to red is **Lemon Juice**.

---