Verified answer

Answer:

Option 4 sc

Sc, due to the poor shielding of d-orbital, the Zeff for Sc becomes high, and hence the ionisation energy is high

have a great day

Explanation:

Going down the group, ionization energy decreases and moving across a period ionization energy increases, so scandium has the highest ionization energy.

Therefore,the correct option is SC(4)

Hope it's helpful...