Please choose the correct answer to the question: Oxygen reacts with iron to produce rust and with hydrogen to produce water. Which statement describes both reactions?

Answer1: A different mixture is formed in each case. Answer2: A different solution is formed in each case. Answer3: Both a change of state and of elements is involved. Answer4: New molecules are formed but the same elements exist.

Answer format: answer1/answer2/answer3/answer4
Answer: answer4