How do i do this, please. THANK YOU

Astudent reacts 13 moles of iron with 21 moles of oxygen according to the following equation:

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 might this scientific phenomena be explained? a paper clip floats on water.