Is the law of conservation of matter followed in the reaction below? HELP!

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

The half-life of a certain element is 100 days. how many half-lives will it be before only one eighth of this elementremains?

Which orbitals form a pi bond? a. the s orbital and three p orbitals b. the s orbital and two p orbitals c. overlapping p orbitals d. overlapping hybrid orbitals