Which principle best explains how this thermometer works?
(1) A liquid changes to a gas when heated.
(2) A gas changes to a liquid when heated.
(3) A liquid expands when heated and contracts when cooled.
(4) A liquid contracts when heated and expands when cooled.

The thermometer works on the principle of "zero'th law of Thermodynamics". This law states that if two bodies are in thermal equilibrium with another body, then they must also be in thermal equilibrium with each other

Explanation:

i belive its (3)

in the analysis of systems that involve fluid flow, we frequently encounter the combination of properties u and pv.

the formula mass of a molecule or a compound is the sum of the atomic weights of the atoms in its empirical formula

(that's what i know about formula mass)