Question

which of the following will change between isotopes?
electrons
neutrons
nuclei
protons
electron cloud
atomic number
mass number
what is the definition of theory?
a system of ideas that is supported by a large body of evidence
a factor that changes as a result of manipulating other factors
an explanation based on observation
the process of using the senses to obtain information
a factor that is manipulated

Explanation:

First Question (Isotopes):

Isotopes are atoms of the same element with the same number of protons (atomic number) but different numbers of neutrons. This difference in neutrons leads to a different mass number (since mass number = protons + neutrons). Electrons, electron cloud, and atomic number remain the same for isotopes. Nuclei composition changes due to neutron variation, but the key subatomic particle that varies between isotopes is neutrons, and mass number also changes as a result.

A theory in science is a well - supported system of ideas. The option "a system of ideas that is supported by a large body of evidence" matches this definition. The other options: "a factor that changes as a result of manipulating other factors" is a dependent variable, "an explanation based on observation" is a hypothesis - like, "the process of using the senses to obtain information" is observation, and "a factor that is manipulated" is an independent variable.

Answer:

neutrons, mass number (the checkboxes for "neutrons" and "mass number" should be selected)

Second Question (Definition of Theory):