An alkali is titrated against an acid with methyl orange as indicator , which of the following is a correct combination?

Options

A. `{:( " Base " , " Acid" , "End point ") ,( " Weak " , " Strong" , " Colourless to pink "):}`
B. `{:( " Base " , " Acid" , "End point ") ,( " Strong " , " Strong" , " Pinkish red to yellow "):}`
C. `{:( " Base " , " Acid" , "End point ") ,( " Weak " , " Strong" , " Yellow to pinkish red "):}`
D. `{:( " Base " , " Acid" , "End point ") ,( " Strong " , " Strong" , " Pink to colourless "):}`

Answer

To solve the question regarding the titration of an alkali against an acid using methyl orange as an indicator, we need to analyze the properties of the indicator and the nature of the reactants involved.

### Step-by-Step Solution:

1. **Understanding Methyl Orange Indicator**:
- Methyl orange is an acid-base indicator that changes color based on the pH of the solution.
- It turns from red (in acidic conditions, pH < 3.1) to yellow (in basic conditions, pH > 4.4).

2. **Identifying the Nature of the Reactants**:
- In this titration, we have an alkali (base) and an acid.
- The alkali will be present in the conical flask, and the acid will be titrated into it.

3. **Starting Color of the Solution**:
- Since the alkali is in the flask, the initial color of the solution will be yellow (because the solution is basic).

4. **Titration Process**:
- As we add the acid to the alkali, the pH of the solution will gradually decrease.
- When the solution reaches a pH around 3.1 to 4.4, the color will change from yellow to pinkish-red.

5. **Determining the Endpoint**:
- The endpoint of the titration occurs when the solution becomes slightly acidic, which will show a pinkish-red color due to the presence of the acid.

6. **Analyzing the Options**:
- **Option 1**: Base weak, acid strong, endpoint colorless to pink - Incorrect (the starting color should be yellow).
- **Option 2**: Base strong, acid strong, endpoint pinkish red to yellow - Incorrect (the endpoint should be from yellow to pinkish-red).
- **Option 3**: Base weak, acid strong, endpoint yellow to pinkish red - Correct (the starting color is yellow and it turns pinkish-red).
- **Option 4**: Base strong, acid strong, endpoint pink to colorless - Incorrect (the endpoint should not be colorless).

7. **Conclusion**:
- The correct combination for the titration of an alkali against an acid using methyl orange as an indicator is **Option 3**: Base weak, acid strong, endpoint yellow to pinkish red.