Atkins+e8a. 12. +At+what+radius+does+the+probability+density+of+a+ground-state+electron+in+the+H+atom+fall+to+50%+of+its+maximum+value?
a) r = 0. 5a₀
b) r = a₀
c) r = 2a₀
d) r = 3a₀