Which element would release the most energy while adding an electron to a neutral atom in the gas phase?

Which of the following is most likely true about water in chemical solutions?

Light waves travel than sound waves.

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!