What is the critical temperature at which hydrogen can begin to fuse into helium in the core?

May someone me with these science questions

Which of these is a physical property

I'm learning about the periodic tables and what each subject's configuration is. for example, hydrogen is 1s^1, but i don't understand how you get that. can someone me understand how to figure out how to figure this out? sorry if the question makes no sense, but it would really a lot if you could me understand! you so much if you can!