Number of unpaired electrons in $Mn^{2+}$ is

Given below are two statements: one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$.
Assertion $(A)$: The first ionization enthalpy of $3d$ series elements is more than that of group $2$ metals.
Reason $(R)$: In $3d$ series of elements,successive filling of $d$-orbitals takes place.
In the light of the above statements,choose the correct answer from the options given below:

The correct statement about iron includes:
$I$) The highest oxidation state of iron is $+ 6$ in $K_2FeO_4$.
$II$) The iron shows $+ 2$ oxidation state with six electrons in the $3d$ orbitals.
$III$) The common oxidation state of iron is $+ 3$ with five unpaired electrons in the $3d$ orbital.

Which of the following elements show $+7$ oxidation states?

The set that contains the atomic numbers of only transition elements is -

Explain the variations in atomic radii of transition elements along the period. The following table provides data for the first transition series:

Element	Sc	Ti	$V$	Cr	Mn	Fe	Co	Ni	Cu	Zn
Metallic Radius $M$ (pm)	$164$	$147$	$135$	$129$	$137$	$126$	$125$	$125$	$128$	$137$