Pls help me on my quiz for chemistry

Avariable that is not being directly tested during an experiment should be changed varied experimented controlled

Mary is conducting an experiment on how pollution affects plant growth. how can she ensure that her data are reliable?

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!