1. The problem statement, all variables and given/known data The expectation value <r> of the electron-nucleus separation distance 'r' is: <r> = ʃ r |ψ|² dV. (a) Determine <r> for the 1, 0, 0 state of hydrogen. 3. The attempt at a solution Right, I've obtained the value for ψ = (1/πa³)^1/2 exp(-r/a) I then replace dv by 4πr² dr. I then put all of that in the equation above and try to integrate but I cant seem to go any further from here. Any help? Thanks very much.