Among the following options,identify the element which exhibits the greatest number of oxidation states.

Fill in the blanks:
$(a)$ The ground state electronic configurations of $Cr$ and $Cu$ are .......... and ..........,respectively.
$(b)$ Transition elements exhibit certain characteristic properties due to partially filled $d$-orbitals.
$(c)$ The general electronic configuration of transition elements is .......... .

The spin only magnetic moment of $Mn^{4+}$ ion is nearly (in $BM$)

Given below are two statements: one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$. Assertion $(A)$: In aqueous solutions $Cr^{2+}$ is reducing while $Mn^{3+}$ is oxidising in nature.
Reason $(R)$: Extra stability to half-filled electronic configuration is observed than incompletely filled electronic configuration.
In the light of the above statement,choose the most appropriate answer from the options given below:

Which element among the following is ferromagnetic?

The $CORRECT$ ionisation energy order is