What does mg stand for in chemistry

What are the first three quantum numbers for the electrons located in subshell 2s?

Answer asap need by wednesday morning calculate the ph of 0.036m naoh best answer will be brainliest

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!