Draw resonance structures to show in which position nitrobenzene will nitrate to form dinitrobenzene

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!

The fact that the total amount of energy in a system remains constant is a(n)

Give more examples of this type of heat transfer: