The incorrect statement among the following is:

We evaluate the validity of each statement:

1. Option A: The orbital angular momentum of an electron is given by $\sqrt{l(l+1)}\frac{h}{2\pi}$. For an 's' orbital, the azimuthal quantum number $l = 0$, so the angular momentum is zero. This statement is Correct.
2. Option B: An atomic orbital is defined by three quantum numbers: principal ($n$), azimuthal ($l$), and magnetic ($m_l$). An electron within that orbital is further distinguished by the spin quantum number ($m_s$), requiring four quantum numbers total. This statement is Correct.
3. Option D: By convention in quantum mechanics, the magnetic quantum number $m_l = 0$ is assigned to the $d_{z^2}$ orbital (which lies along the z-axis). This statement is Correct.
4. Option C: Since options A, B, and D are correct, this option must be the Incorrect statement. In the context of this NEET question, this option typically presents an electronic configuration diagram for Nitrogen ($1s^2 2s^2 2p^3$) that violates Hund's Rule (e.g., by pairing electrons in the 2p orbitals before singly occupying them) or Pauli's Exclusion Principle.