Its acidity has been increased. More oxygen has been dissolved in it. Impurities have been removed. Its molecules have higher chemical energies.
I am hesitating between 4 options to answer the following question, which option should I choose?
Question: A gasoline is advertised as "releasing fewer pollutants" when it is used in cars. For this claim to be accurate, what has most likely happened to the gasoline?
Possibilities:
- Its acidity has been increased.
- More oxygen has been dissolved in it.
- Impurities have been removed.
- Its molecules have higher chemical energies.

Impurities have been removed.