Answer:
5d
Step-by-step explanation:
Hafnium
[Xe]6s2 4f14 5d2
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d2
Above is the full electron configuration of Hf. It can be seen that it has the same d2 outermost electron configuration as Ti. Hence they belong to the same group in the periodic table.