The way to recognize an electron transfer reaction from a balanced chemical equation is:

(a) To draw a dot diagram of every reactant and product and see that the octet rule is not obeyed for some atoms.

(b) To assign oxidation states to every atom and see if they always add to give the charge of the molecule.

(c) To assign oxidation states to every atom and see if any change on going from reactants to products.

(d) To assign oxidation states to every atom and see if any go from positive to negative or negative to positive.