Which element from the following possesses half-filled $d$-orbitals either in expected or in observed electronic configuration?

The oxide of a metal $(R)$ can be reduced by the metal $(P)$,and metal $(R)$ can reduce the oxide of metal $(Q)$. Then the decreasing order of the reactivity of metals $(P)$,$(Q)$,and $(R)$ with oxygen is:

Observe the following data ($ \Delta_i H_1, \Delta_i H_2 $ and $ \Delta_{eg} H $ represent the first,second ionisation enthalpies and electron gain enthalpy respectively).

Element	$ \Delta_i H_1 $ $( kJ \ mol^{-1} )$	$ \Delta_i H_2 $ $( kJ \ mol^{-1} )$	$ \Delta_{eg} H $ $( kJ \ mol^{-1} )$
$ I $	$ 520 $	$ 7300 $	$ -60 $
$ I.I $	$ 490 $	$ 3051 $	$ -48 $
$ III $	$ 1681 $	$ 3374 $	$ -328 $
$ IV $	$ 2372 $	$ 5251 $	$ +48 $

Using the data,identify the most reactive metal.

Which pair of elements has the same chemical properties?

Which of the following is the most electropositive element?

Which of the following is the most basic oxide?