What does an Ionization Detector respond to?

The Ionization Detector responds to ionized particles from combustion, which is the correct choice. This type of smoke detector uses a small amount of radioactive material to ionize the air within the sensing chamber. When combustion occurs, particles released into the air from the fire disrupt this ionization process. The detector senses the changes in ionization, which triggers the alarm.

In contrast, other options do not align with the operational principles of an Ionization Detector. For example, it does not specifically respond to visible smoke alone; it is designed to detect the particles generated by combustion, which can include smoke that may not be visible to the naked eye. Similarly, it is not solely responsive to heat variations, as that function is typical of heat detectors rather than ionization detectors. The option regarding water vapor is also inaccurate since ionization detectors are not designed to detect humidity or moisture in the air. Their primary function is to sense ionized particles resulting from combustion, thereby providing early warning of a fire.