Question

which is the best location for storing radioactive wastes? in the sand of a remote island in chambers carved into the rock of a mountain in the lava tubes of an active volcano in natural caverns formed by the action of a river

Explanation:

Storing radioactive waste requires isolation from the biosphere for long - term safety. Chambers carved into mountain rock provide stable, impermeable, and isolated environments. Sand on a remote island can be affected by erosion and sea - level rise. Active volcanoes are unstable and could release waste. River - formed natural caverns are at risk of water intrusion and collapse.

Answer:

in chambers carved into the rock of a mountain