To solve this question, the user needs to know the basic principles of thermodynamics and the concept of heat transfer through radiation. When an object is heated, it emits thermal radiation in the form of electromagnetic waves. This radiation carries energy away from the object, causing it to cool down.
Now, let's go through each option and explain why it is right or wrong:
A. Electrons: This option is incorrect because the emission of electrons is not a form of heat transfer. Electrons are negatively charged particles that are involved in electrical conduction and chemical reactions, but they do not play a role in thermal radiation.
B. Radio waves: This option is incorrect because radio waves are a type of electromagnetic radiation, but they have a much lower frequency and longer wavelength than the type of radiation emitted by a hot object. Radio waves are typically used for communication and broadcasting, but they are not involved in heat transfer.
C. Visible light: This option is incorrect because visible light is also a type of electromagnetic radiation, but it has a much higher frequency and shorter wavelength than the type of radiation emitted by a hot object. Visible light is responsible for the colors we see, but it is not involved in thermal radiation.
D. Infra-red radiation: This option is correct. Infra-red radiation is a type of electromagnetic radiation that has a frequency lower than visible light but higher than radio waves. It is the type of radiation that is emitted by a hot object as it cools down. Infra-red radiation is responsible for the heat we feel when we stand near a hot object, such as a fire or a stove.
Therefore, the correct answer is: D. Infra-red radiation.