Question

which of the following variable physical properties are utilized in mercury thermometers? density electrical resistance expansion

Explanation:

Mercury thermometers work based on the principle of thermal expansion (liquid expansion with temperature increase). Density and electrical resistance are not the primary physical properties used in mercury thermometers. Density relates to mass/volume and electrical resistance to current flow, neither of which is the core principle for temperature measurement in mercury thermometers.

Answer:

O expansion