21. Why are radioactive nuclei unstable? a. There is not the proper neutron to proton ratio resulting in a stable nucleus
b. There is too much energy stored in the bonds between atoms
C. They need to gain/lose electrons to have a full valence energy level
d. Protons reverse their charges and begin to repel one another

a. There is not the proper neutron to proton ratio resulting in a stable nucleus

Explanation:

Radioactive nuclei are unstable because they do not have a proper neutron to proton ration that can result in a stable nucleus for them.

in 1783 cavendish was working with his hydrogen gas and found that when he burned it and condensed the vapor it was water. this was very significant since it disproved the greek theory of elements completely since water was not a simple substance but the product of two gases. it was lavoisier who hearing of the experiment gave cavendish's gas the name hydrogen ("water-producer") and added that hydrogen burned by combining with oxygen and that water was a hydrogen-oxygen combination.

explanation:

1.solid

2.carbon dioxide

3.helium