Did I get these right? If not, please explain

Blank liquids and gases exert a buoyant force on objects placed in them

What are atoms of the same element with varying number of neutrons

30 points - when can a theory be modified if a new type of technology allows for new observations that raise new questions? a. immediately, while the questions about the theory are being asked b. after new hypotheses related to the theory are tested in experiments c. only after the new observations disprove all parts of the theory d. while scientists begin to think about how the theory could improve