For the oxidation-reduction reaction equation given here 4ga+p4 indicate how many electrons are transferred in the formation of one formula unit

The reaction given is:

4Ga + P4 ---> 4GaP

The oxidation number of the reactants is zero, because they are pure elements.

The P in compounds may have oxidation states 3- or 5-. Gallium may only have oxidation state 3+.

Then, to be neutral in GaP the oxidation states are 3+ for Ga and 3- for P.

And the transference of electrons can be see in this oxidation - reduction equations:

Ga (0) - 3 e-    > Ga (3+)

P (0) + 3e- ---> P (3-)

So, for one formula unit, 3 electrons have been transfered from each Ga atom to P atom to form one GaP unit.

3 electrons.