The gallionella bacteria reaction
that is Fe2+ → Fe3+ is example of oxidation reaction (answer A)
Step-by-step explanation
oxidation reaction reaction occurs when electrons are lost during reaction by a molecule or ion or atom. when oxidation occurs the oxidation state of the molecule or ion or atom increases. For this reason Fe2+ → Fe3+ is a oxidation reaction since the oxidation state move from oxidation state 2 to 3