Pros of using mixtures and solutions in a science lab

Yes she is correct. the answer is completely correct

  super sorry but i dont know lo

Ithink about 50 % of an original isotope's number of atoms remain

Firstly, the planetary model of the atom  failed  to explain why individual atoms produce discrete  line spectra. in fact, according to rutherford's model, each individual atom should produce a  continuous  line spectrum. the second flaw to his model was the fact that electrons orbit the nucleus in a circular fashion.