Which form of energy is generally invisible to the eye but can be measured in terms of temperature?

Thermal energy is the correct choice as it refers to the energy that comes from the temperature of matter. It is related to the motion of atoms and molecules within substances. Although we cannot see thermal energy directly, its effects can be observed through temperature changes.

For instance, when you heat a metal object, you may not see the energy itself, but you can measure the increase in temperature, which indicates that thermal energy has been added to the object. In other words, thermal energy is an intrinsic form of energy that manifests as heat, making it measurable via temperature scales such as Celsius or Fahrenheit.

Conversely, kinetic energy pertains to the energy of motion and can be observed when an object is moving. Potential energy deals with the energy stored in objects due to their position or arrangement, which is also not directly measurable in terms of temperature. Mechanical energy combines kinetic and potential energy in moving systems and is not specifically linked to temperature.