Answer: The sub shells which behave as valence orbitals are '5d' and '6s'.
Step-by-step explanation:
Valence orbitals are defined as the outermost orbitals from which an atom looses or gains electrons to attain stability.
Metals are defined as the elements which loose electrons to attain stability.
Non-metals are defined as the elements which gain electrons to attain stability.
Hafnium is the 72th element of the periodic table having electronic configuration of
![[Xe]6s^24d^(10)5d^(2)](https://img.qammunity.org/2018/formulas/chemistry/high-school/zzay8pdvt5yufcxw23youkxvzxhrkarrp8.png)
This element is a transition element and shows variable oxidation of +2 and +4.
Thus, hafnium may loose electrons from either '6s' subshell of from '5d' subshell.
Hence, the sub shells which behave as valence orbitals are '5d' and '6s'.