If we start with 1200 atoms of a radioactive substance how many would remain after three half-lives

Mary is conducting an experiment on how pollution affects plant growth. how can she ensure that her data are reliable?

At element makes up all organic compounds?

Choose all the answers that apply. fluorine (f) has an atomic number of 9 and an atomic weight of 18.99. fluorine has a. 9 protons b. 10 neutrons c. 18 electrons d. an atomic mass of 19 e. at least one isotope