How long do you think it would take to create a canyon as deep as the Grand Canyon? Explain your reasoning.

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.

Which statement is best described as a atom

In 2002, the rare earth elements mine in mountain pass, california was closed because