Can someone explain?

Which of the following statements is true? a. elements in the last period are radioactive. b. atomic weight is the same as atomic mass. c. elements in the same group have the same number of electron shells. d. atomic number equals the number of neutrons in the nucleus of an atom.

Why is the melting of ice a physical change ?

One student said that the investigation was not valid (a fair test). write a plan for the investigation that includes improvements to the method and apparatus