At the beginning of the chapter, is there a reason why the SS guard ordered the men and women to be separated?

They had different sections in the camp for men and women. It was a matter of convenience for the camp, and it was another way to create psychological distress. Additionally, they knew that if they were separated from the women, that the men would not be as likely to fight back. In this particular case, the women and children are killed. This is the reason Eliezer is told to lie about his age and say he's eighteen.