Radioisotopes are commonly used in which of the following applications?

Radioisotopes are indeed commonly used in nuclear power generation. In this application, specific isotopes such as uranium-235 or plutonium-239 undergo fission reactions to produce heat, which is then used to generate electricity. The isotopes release a significant amount of energy when their nuclei split, making them suitable for generating the high temperatures required in power plants to produce steam for turbine operation.

Other applications, while they may use various technologies and methods, do not primarily involve radioisotopes. For instance, food drying generally utilizes heat rather than radioactive elements; water purification can involve methods like filtration or chemical treatment; and scent detection typically relies on sensors and does not use radioactive materials. Thus, nuclear power generation stands out as the primary and well-established use of radioisotopes among the options provided.