Ionisation Enthalpy, Oxidation States — Prelims Questions

Which of the following statements regarding the ionisation enthalpy of 3d transition elements is INCORRECT?

Which of the following transition elements exhibits the highest oxidation state in its compounds?

Which of the following statements correctly explains why $Cu^+$ disproportionates in aqueous solution?

Which of the following elements has an exceptionally high third ionisation enthalpy ($IE_3$)?

Which of the following statements is TRUE regarding the oxidation states of transition elements?

The first ionisation enthalpy ($IE_1$) values (in kJ/mol) for the 3d series elements are given below. Identify the element that shows an unexpected dip in the general trend of increasing $IE_1$ and provide the reason. Sc (631), Ti (658), V (650), Cr (652), Mn (717), Fe (762), Co (758), Ni (736), Cu (745), Zn (906)