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Question

Which of these orbital designations is incorrect.

A) 4s

B) 4f

C) 2d

D) 5p

Answer 1

I'm pretty sure it is 2d.

Answer 2

Yes, it's 2d.  That's because there are no d-orbitals in the second energy level.

You may recall the set of four quantum numbers that can be used to identify each and every electron in an atom.

The principle quantum number is the value of n.  L is the azmuthal quantum number, which is the the one that defines the sub-level, and can have values of 0 to n-1.  When n is equal to 2, then L can have values of 0 and 1 which correspond to the s-sublevel and the p-sublevel, but not the d-sublevel.  For the d-sublevel, L would have to have a value of 2 which can only happen when n=3.