Which EMW can humans see?

What type of matter is made of only one kind of atom

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!

How many moles of co2 are produced during the complete combustion of 3.6 moles of c2h6