Why do posisons collect more in carnivores than in herbivores?

The simple answer is bioaccumulation resulting from biomagnification. Carnivores consume organisms at higher trophic levels, and thus "poisons," such as heavy metals accumulate in these organisms at levels greater than those found in plants. Moreover, such chemicals typically accumulate in the fatty tissues of carnivores, such as the nervous, lymphatic, endocrine, and reproductive systems.

the correct option is c.

isotopes refers to different forms of the same element with the same atomic number but different mass number as a result of difference in their neutron numbers. isotopes have different relative atomic mass but share the same chemical properties.