When you eat sugar (C₁₂H₂₂O₁₁), it is eventually converted into CO₂ and H₂O, which you exhale.

If you exhale onto a cold window, the window fogs up.

(a) What chemical change is being mentioned here?

(b) What physical change is being mentioned here?

(c) CO₂ is a solid that sublimes at –78°C.

Temperatures on planet Earth almost never get this cold. What does that tell you about the fog on the window?