The best way to react to a wrong answer given by a student is :

To scold him for not having learnt the lesson
To explain why the answer is wrong
To ask another student to give the correct answer
To ignore the wrong answer and pass on the next question

The correct answer is: B. To explain why the answer is wrong.

When a student gives a wrong answer, it is important to first understand why they gave that answer. Did they misunderstand the question? Did they not know the material? Once you understand the reason for the wrong answer, you can then explain why it is wrong and provide the correct answer. This will help the student learn from their mistake and improve their understanding of the material.

Scolding a student for giving a wrong answer is not an effective way to help them learn. It will only make them feel embarrassed and ashamed, which can lead to them avoiding asking questions or participating in class. Asking another student to give the correct answer is also not a good idea, as it does not give the student who gave the wrong answer a chance to learn from their mistake. Ignoring the wrong answer and passing on to the next question is also not helpful, as it does not allow the student to get the help they need to understand the material.

The best way to react to a wrong answer is to explain why it is wrong and provide the correct answer. This will help the student learn from their mistake and improve their understanding of the material.