Answer: The sentence that provides the best use of passive voice is the second one: "Water is formed by two molecules of hydrogen and one of oxygen".
Step-by-step explanation: Passive voice is widely used in English; however, in some cases, it is not recommended to use it. For example, passive voice needs to be avoided when it makes a sentence too wordy or when it affects the natural flow of the sentence. In that way, the use of the passive voice in "The door was opened by Katrina when the bell was rung by Lana", "The story was read by each person in the class, taking turns" and "This paper airplane was folded by Andrea and thrown at me" makes the sentences sound unnatural. On the other hand, "Water is formed by two molecules of hydrogen and one of oxygen" offers the best use of passive voice since it is recommended to use passive voice when we talk about general truths, that is to say when we make reference to a fact, such as the composition of water in the second sentence.