In the presence of a magnetic field a d-orbital in an atom is
A Five fold degenerate
B Three fold degenerate
C Seven fold degenerate
D Non degenerate

In the presence of an external magnetic field, the orbitals of each sub shell will take up different orientations. These orientations are represented using the magnetic quantum number "m" which relies on the angular quantum number "l". Each of these orientations refer to an orbital and hence the number of orbitals in the d sub shell in the presence of magnetic field can be found out as follows,

  Angular quantum number, l = 2
  So, magnetic quantum number, m = -2 to 2 = -2, -1, 0, 1, 2
  Therefore, Number of orbitals = 5 orbitals

Hence, the d orbital is five fold degenerate.