[nobOdy98]

I am royally stuck on a problem in my quantum class.

Here is the question:
Write Down an expression for the radial distribution function of a 3s electron in a hydrogenic atom and determine the radius at which the electron is most likely to be found?


I am completely lost on this problem and am not even sure where to start. 

[FeLiXe]

the radial distribution function is the wave function integrated over phi and psi
for an s-orbital you just have to multiply the function by 4 r^2 pi
the global maximum of this will be the second answer

[nobOdy98]

Why am I leaving out the r component in the integration?

[Yggdrasil]

Your wave function is function that depends on three variables, r, phi and psi.  By integrating over phi and psi, you obtain a wavefunction that depends only one value, r.

If you were to integrate over all possible values of phi, psi, and r, you would 1 by definition because the probability that your electron is somewhere is one.