What is a valence electron and why are they so important to a chemist?

Iknow the answer to 13 is b and 14 is d. i just need to know why the correct answers are correct

1) these are barrel shaped microtubules in most animal cells, that organize the spindles during cell division

Will give ! what are the advantages and disadvantages of nuclear power? check all that apply. one advantage of nuclear energy is that it does not produce carbon dioxide emissions. storage of nuclear waste is a short-term problem associated with nuclear energy. the problem with uranium mining is that a large quantity of uranium must be extracted to meet energy needs because the energy release from uranium fission is so low. safe operation of a nuclear power plant can be jeopardized by a human mistake.