Answer
System (iii)
Work Step by Step
In an endothermic process the system gains heat from its surroundings, so the sign of q is positive. This is only true for system (iii).
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.