Question

Which of the subshells in the electron configuration of Hf behave as core orbitals
Check all that apply

1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d

Answer 1

Hf is [Xe]4f14 5d2 6s2
All but 5d2 and 6s2 are core.
http://www.webelements.com/hafnium/atoms.html