Step 1: Changing sentence into indirect speech.
This is an imperative sentence, so the reporting verb should be "told" or "ordered". The sentence in direct speech has a command, and when converting it to indirect speech, we use "not to" for negative commands. Step 2: Indirect speech for sentence (ii):
The teacher told the boys not to make a noise in the class. Step 3: Conclusion.
The indirect speech form of the given sentence is: The teacher told the boys not to make a noise in the class.