In which of the following fields is radioisotopes not used?

Analyze the question: We need the field where radioisotopes are not used.

Concept: Radioisotopes are unstable isotopes that emit radiation. Their uses include:

• Medicine: Iodine-131 for thyroid treatment and diagnosis, Cobalt-60 for cancer radiotherapy, and sterilising surgical equipment.
• Oil industry: Tracers are used to detect leaks in pipelines and to trace oil flow and the movement of fluids in wells.
• Agriculture: Phosphorus-32 is used as a tracer to study how plants absorb fertilisers. Radiation is also used to induce crop mutations, control pests, and preserve food.
• Weather forecasting: This relies on meteorological instruments such as barometers, thermometers, anemometers, hygrometers, weather balloons, radar, and satellites. These measure pressure, temperature, wind, and humidity, and do not depend on radioisotopes.

Solution:

• A: Medicine uses radioisotopes, so it is not the answer.
• B: The oil industry uses radioisotopes, so it is not the answer.
• C: Agriculture uses radioisotopes, so it is not the answer.
• D: Weather forecasting does not use radioisotopes in any standard application, so it is the answer.

Tip: For "not used" questions, recall the classic uses of radioisotopes: medicine, agriculture, industry (tracers and thickness gauges), archaeology (carbon dating), and food preservation. The option that does not fit any of these is your answer.