What is the difference between a physical change and a chemical change? give examples for both

Which diagram shows the correct way to represent an ionic compound of magnesium oxide?

Harry lives in a city, and he has a lung condition known as asthma. on certain days, harry has to stay inside because pollutants in the air make it difficult for him to breathe. which of these pollution sources are nonpoint sources that might bother harry if he goes outside? choose the two that apply.

The most common form of matter in the universe