Melting gold bars is the process that involves an increase in entropy
I got on here because I don't understand the question but I did my best to answer because I noticed you asked 3 days ago. IF I'm right the answer is D. My diagram shows
A at -50 °C
B at 0 °C
C at 50 °C
D at 100 °C (gas to liquid or liquid to gas)
And E at 150 °C
So I hope I'm right because I'm answering the same question.