Correct Answer: The mother asked her son why he was not doing his homework.

Solution : The second option is the correct choice.

The steps of conversion are as follows:

• The reporting verb "said" is changed to "asked".
• "Why" will be used as a conjunction because we know that in an interrogative sentence with a question word, the question word itself becomes the conjunction.
• "You" (a second-person pronoun) is changed to "he" (a third-person pronoun).
• The present continuous tense is changed to the past continuous tense.

Therefore, the correct answer is: "The mother asked her son why he was not doing his homework."