Which metal wire is used as a conductor of electricity?

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: Generally, $3d$ transition metals have high melting points.
Reason $R$: Involvement of $3d$-electrons in addition to $4s$-electrons in the interatomic metallic bonding.
In light of the above statements, choose the most appropriate answer from the options given below:

Which of the following represents the decreasing order of the second ionization enthalpy $(I.P_2)$?

The increasing order of magnetism of $(I)$ $MnSO_4 \cdot 4H_2O$,$(II)$ $FeSO_4 \cdot 7H_2O$,$(III)$ $NiSO_4 \cdot 6H_2O$,and $(IV)$ $CuSO_4 \cdot 5H_2O$ is:

How many unpaired electrons are there in $Ni^{2+}$?

Which of the following ions has the highest magnetic moment?