What element is used for shiny trim on cars

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.

There are main groups in the modern periodic table of elements

Compare the valence electron configuration of the nobles gas elements seen here. what statement is correct?