Achemistry instructor performed the following mystery demonstration. just before the students arrived in class, she heated some water to boiling in an erlenmeyer flask. she then removed the flask from the flame and closed the flask with a rubber stopper. after the class commenced, she held the flask in front of the students and announced that she could make the water boil simply by rubbing an ice cube on the outside walls of the flask. to the amazement of everyone, it worked. give an explanation for this phenomenon.

Decrease in pressure

Explanation:

Boiling depends both an temperature and pressure, water up on the mountain boils at a much lower pressure than water boiling below the mountain level. When water boils, water vapor escape the surface of the liquid building pressure above the water. putting ice below the flask lowers  the pressure. This lowering of the pressure causes more liquid to boil.

the answer is:  

line graphs show patterns in data with variables that change over time; whereas, circle graphs show data as parts out of a whole (such as out of 100%).