Answer: b) tracing the movement of cadmium isotopes in test animals
Explanation: Cadmium is a type of soft metal that is found to be accumulating in the animal body. The appropriate way for finding the place of accumulation is by tracking the cadmium isotope's path in the body of test animal.
By tracing the movement of cadmium , the location where it stops and gets deposited can be reached and then best possible solution can be extracted to resolve the issue by researchers.
Other options are incorrect because finding acidity in water and size of cadmium is not relevant solution. The bond between the cadmium atoms also don't provide any relevance with the given situation.Thus, the correct option is option(b).