Radioactive elements include all those elements whose nuclei contain more than
1.
83 amu
83 nucleons
83 neutrons
83 protons

4: 83 protons

Explanation:

In elements with more than 83 protons, all of the isotopes are radioactiv

2h2o2--> 2h2o + o2

this reaction is of the spontaneous decomposition of hydrogen peroxide down into water and oxygen.

add 2 molecules of hydrogen peroxide and 2 molecules of water. since oxygen is naturally diatomic, the total number of atoms of each element is now the same on both sides of the equation so it is balanced.

this may not be entirely correct but let me know.

space exploration has led to the development and technological improvement of many everyday items. (if this answer is wrong i will find the right answer) : )