Which of the following represents the correct order of the given properties?

Identify the element having the highest ionization enthalpy among the given options.

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:

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

The most abundant transition metal in the human body is

The ions of $d$-block elements are paramagnetic because.....