Determine the quantity (g) of pure CaCl2 in 7.5 g of CaCl2•9H2O

Calculate the frequency of a wave in a spring toy. the wave has a speed of 1.1 meters per second and a wavelength of 0.1 meters. *

The table compares the number of electrons in two unknown neutral atoms. comparison of electrons atom number of electrons a 9 d 11 use this information to determine the number of valence electrons in the atoms. which of the following correctly compares the stability of tthe table compares the number of electrons in two unknown neutral atoms. comparison of electrons atom number of electrons a 9 d 11 use this information to determine the number of valence electrons in the atoms. which of the following correctly compares the stability of the two atoms? both are unreactive. both are highly reactive. a is unreactive and d is reactive. a is reactive and d is unreactive.

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!