What is the lowest possible value of n for a d atomic orbital?

Answer is: the lowest possible value of n is 3, that is 3d atomic orbital.

The principal quantum number (n) is one of four quantum numbers which are assigned to each electron in an atom to describe that electron's state.

The principal quantum number shows the most probable distance of the electrons from the nucleus.

For n=3, there are 3 orbitals: 3s, 3p and 3d.