Do you understand what they are asking?

Which of the following physical properties can be used to measure temperature using a thermometer?
volume
pressure
density
viscosity

Im guessing they are talking about viscosity but I don't quite fully understand it

Think about the thermometer. It is a sealed capillary tube with mercury or color alcohol inside. When the bulb is heated, the liquid expands, and the only place it has to go is up the tube. The pressure inside is the same, the density and viscosity (over a few degrees, at least) are essentially the same so what's left?

http://en.wikipedia.org/wiki/Thermometer

Yes, I understand the question. The question is asking which physical property can be used to measure temperature using a thermometer from the given options: volume, pressure, density, and viscosity.

To answer the question, we need to understand what each of these properties represents and how they relate to temperature.

1. Volume: Volume refers to the amount of space an object occupies. Although temperature can affect the volume of certain substances, it is not a direct measure of temperature.

2. Pressure: Pressure is the force exerted on a specific area. While temperature can influence the pressure of a gas, it is not a direct measure of temperature either.

3. Density: Density is the mass per unit volume of a substance. It is not a direct measure of temperature and is influenced by factors other than just temperature, such as composition and pressure.

4. Viscosity: Viscosity is a measure of a fluid's resistance to flow. It is influenced by temperature, with most substances becoming less viscous as temperature increases. Although viscosity can be influenced by temperature, it is not commonly used as a direct measure of temperature using a thermometer.

Therefore, out of the given options, none of them is primarily used to directly measure temperature using a thermometer.