Question

Why do we breathe out on spectacle glasses to clean them?

Answer 1

when we out on glasses of spectacles, the moisture of our mouth settles on the surface of glasses which cools down & forms tiny droplets to make it wet, which helps us to clean the spectacles

Answer 2

Answer:
During exhalation (or breathing out), carbon dioxide is released along with water vapours. If one breathes out onto glass, the released water vapours collide with the surface of the glass, thereby making it cooler. As a result, the water vapours present in the air surrounding get attached to the glass surface. Consequently, the glass becomes clean after wiping it.