what is the number of electrons of C2H5OH + 3 O2 = 2 CO2 + 3 H2O?

Answer 1

Supposing you are asking for the total number electrons transferred in the given equation:

All of the elemental oxygen (six atoms) goes from an oxidation state of 0 to 2-, so a total of 12 electrons got transferred.

Answer 2

Do you mean the total number of electrons on each side of the equation? Or the number of valence electrons? Or do you mean the number of electrons transferred in this redox reaction?

Can you clarify what you are after?