Alex saw a rusty old car in an abandoned lot. because he had recently read about chemical reactions, he began to wonder how the rust formed. what happened to cause the rust on the steel car? a. a decomposition chemical reaction took place when the iron in the steel mixed with oxygen to form rust. b. oxygen in the air reacted with the paint on the car and formed rust c. a physical change took place in the steel of the car to form rust d. oxygen in the air chemically combined with iron in the steel to form rust.