What do these two changes have in common?
filtering air to remove dust and pollen
a crayon melting in the sun
A: Both are only physical changes.
B: Both are caused by heating.
C: Both are chemical changes.
D: Both are caused by cooling.
Step 1: Think about each change.
Filtering air to remove dust and pollen is a physical change. The air flows through the filter, and the pollen and dust stay behind. This separates the mixture of air, pollen, and dust. But separating a mixture does not form a different type of matter.
A crayon melting in the sun is a change of state. So, it is a physical change. The crayon changes state from solid to liquid. The crayon is still made of wax, even after it melts.
Step 2: Look at each answer choice.
Both are only physical changes.
Both changes are physical changes. No new matter is created.
Both are chemical changes.
Both changes are physical changes. They are not chemical changes.
Both are caused by heating.
A crayon melting in the sun is caused by heating. But filtering air is not.
Both are caused by cooling.
Neither change is caused by cooling.