Provide your best answer for the following question. Give ONLY the answer, no other words or explanation.
For example:

Answer: <most likely answer, as short as possible; not a complete sentence, just the answer!>.

The question is: A teacher asks her students to examine titles of four scientific articles. Which titled article is specifically about a chemical change?
How Baking Soda Reacts With Vinegar
Article 1: Acid Rain Formation: A Chemical Change in the Atmosphere