Oxidant and reductant strength

The most stable oxidation state is the most reluctant reactant in a redox reaction.
These are marked with asterisks below. Usually elements occur in these oxidation states in nature.

For example sodium occurs as Na(+1) in NaCl, magnesium as Mg(+2) in MgCl₂.

Group 1	Li	Na	K	Rb	Cs
ns¹	+1*	+1*	+1*	+1*	+1*
	0	0	0	0	0

Group 2	Be	Mg	Ca	Sr	Ba
ns²	+2*	+2*	+2*	+2*	+2*
	0	0	0	0	0

Group 13	B	Al	Ga	In	Tl
ns² np¹	+3*	+3*	+3*	+3*	+3
B and Al have ill-defined negative oxidation states				+1	+1*
	0	0	0	0	0

Species containing atoms in oxidation states other than the most stable tend in their redox reactions to achieve the most stable state.
Thus oxidant/reductant strength can be correlated in a qualitative way with the position of a particular oxidation state in the hierarchy of oxidation states.

States below the most stable are good reductants (electron donors) (all Group 1, 2 and 13 elements).
States above the most stable are good oxidants (electron acceptors) (Tl³⁺).
The most stable state is a weak oxidant/reductant (Tl⁺ weak oxidant and weak reductant).