1. first nuclear reactor
curie
2.
neutron
3. splitting of nuclei into lighter elements
atomic mass
4. number of neutrons and protons
becquerel
5. builds heavier elements
fermi
6. discovered radioactivity
fission
7. unit of radiation
fusion
need putting them in

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.

there is none because earth is stationary and flat.