Arrange the following substances in order of increasing tendency to donate electrons with reasons:
α –ketoglutarate, Oxaloacetate, O2, NADP+
, Malate

α- ketoglutarate → NADP+ → Oxaloacetate → O2.

Explanation:

The ability of an molecule or a compound to donate or accept electron can be related to their electron affinity.

The more positive the electron affinity is ; the more likeliness such compound is known to be as an electron acceptor which accepts . Also the less positive the electron affinity is the more likeness such compound will be known to be as an electron donor which donates electron

The electron affinity  of a compound to accept or donate electron can be related to their reduction potential value (Redox Value).

From the information given ; we have α –ketoglutarate, Oxaloacetate, O2, NADP+   and we are to arrange in an  increasing tendency to donate electrons.

i.e from the least tendency to donate electron to the highest tendency to donate electron.

The reduction potential value (Redox Value) of the compounds and molecule given are:

α –ketoglutarate   --->    - 0.38   since  α- ketoglutarate  will react with CO2, it gives isocitrate

Oxaloacetate        >  - 0.18   since  Oxaloacetate will react with two moles of hydrogen ion and electrons respectively to give Malate

O2                        > + 0.82  since  O2 will react with 4 moles of hydrogen ion and electrons respectively to give 2 moles of water

NADP+                 > - 0.32   since NADP+ will react with two moles of electrons and one mole of hydrogen ion to give NADPH

Again; lets recall  the less positive the electron affinity is the more likeness such compound will be known to be as an electron donor which donates electron.

So to arrange the given substances  in order of increasing tendency to donate electrons since we've known their standard reduction potential value (Redox Value); we have the increasing order as:

α- ketoglutarate → NADP+ → Oxaloacetate → O2.