Problem 1: for which of the following activities might you want to hire a chemist?

a. building a garage

b. testing a sample of water from a well

c. finding a comet

d. examining the structure of plant cells
problem 2: which of the following procedures involves a physical change in one of the substances?

a. creating salt by reacting sodium metal and chlorine gas

b. allowing a nail to rust

c. building a model rocket propelled by mixing baking soda and vinegar

d. grinding chalk into a fine powder