What is $\psi$ and what is $|\psi|^2$? What do they represent?

The Heisenberg uncertainty principle is not valid for

Given below are two statements:
Statement $I:$ According to Bohr's model of hydrogen atom,the angular momentum of an electron in a given stationary state is quantised.
Statement $II:$ The concept of electron in Bohr's orbit,violates the Heisenberg uncertainty principle.
In the light of the above statements,choose the most appropriate answer from the options given below:

What is the nature of the solution to the $Schrodinger$ wave equation for multi-electron atoms? How is it handled?

Give the difference between $\psi$ and $|\psi|^2$.

The position of both an electron and a helium atom is known within $1.0 \, nm$ and the momentum of the electron is known within $50 \times 10^{-26} \, kg \, m \, s^{-1}$. The minimum uncertainty in the measurement of the momentum of the helium atom is