Final answer:
Both the assertion and the reason are true statements on their own but the reason does not directly explain why radioactive waste is stored below the earth’s surface. The method and depth of storage can vary and are subject to political, technical, and safety considerations. The correct answer is: B. Both assertion and reason are true but the reason is not the correct explanation of the assertion.
Step-by-step explanation:
The assertion that radioactive wastes are pre-treated and stored in containers 500 m below the earth's surface is not entirely accurate. Precautions are indeed taken to store high-level radioactive waste safely, but the exact depth varies and is not standardly at 500 m. Storage methods include cooling by water and later in special outdoor concrete or steel containers. Long-term underground storage solutions are being explored, such as old salt mines or stable mountains, but a consistent, long-term solution is yet to be universally implemented.
The reason that nuclear radiation can cause mutations at low doses and is lethal at high doses is indeed true. Radiation can cause damage to living tissue, which can lead to mutations and other health problems. Safety measures, regulations, and containment are crucial to prevent harmful exposure, particularly from high-level radioactive waste which can remain hazardous for thousands of years.
Considering the information above, the correct answer is: B. Both assertion and reason are true but the reason is not the correct explanation of the assertion.