The term "atmosphere" is often used interchangeably with the term "mood". In order to answer this question, you have to figure out what "feeling" the reader gets from the new characters and setting in chapter 2. Here are some things to consider:
What is the bunkhouse like physically? Pay attention to detail. Imagine sitting in the bunkhouse. How would it make you feel?
How do Candy and his dog contribute to the reader's feelings about the place?
What about the boss? Look at the way he treats George and Lennie. How does it make the reader feel? Does it make the reader consider anything that might happen in the future?
Remember, you should relate every element you examine back to the feelings it creates in the reader.