Magnetic field at the center (at nucleus) of the hydrogen like atoms (atomic number = z) due to the motion of electron in nth orbit is proportional to
n3z5
n4z
z2n3
z3n5
Bn=μ0In2rn or Bn∝Inrn or B∝fnrn ∴ Bn∝vn/rnrn Hence, B∝vnrn2 ∝(z/n)n2/z2 ∝z3n5