In the series $Sc(Z = 21)$ to $Zn(Z = 30)$ , the enthalpy of atomization of _____ is the lowest

$(a)$ Answer the following questions :

$(i)$ Which element of the first transition series has highest second ionisation enthalpy ?

$(ii)$ Which element of the first transition series has highest third ionisation enthalpy ?

$(iii)$ Which element of the first transition series has lowest enthalpy of atomisation ?

$(b)$ Identify the metal and justify your answer.

$(i)$ Carbonyl $M(CO)_5$  $(ii)$  $MO_3F$

The pair of metal ions that can give a spin-only magnetic moment of $3.9\, BM$ for the complex $[M(H_2O)_6]Cl_2$ is

Out of $\mathrm{Cu}_{2} \mathrm{Cl}_{2}$ and $\mathrm{CuCl}_{2}$, which is more stable and why ?

Correct statement for $CeO_2$ is/are

$(1)$  It is Diamagnetic in nature

$(2)$  It is a good oxidising agen

$(3)$  It is colourless compound

Which of the following element has maximum first ionisation potential