The wave function of an electron of a hydrogen atom in the ground state takes the form \(\psi(r)=A \mathrm{e}^{-r / r_{1}},\) where \(A\) is a certain constant, \(r_{1}\) is the first Bohr radius. Find: (a) the most probable distance between the electron and the nucleus: (b) the mean value of modulus of the Coulomb force acting on the electron; (c) the mean value of the potential energy of the electron in the field of the nucleus.