How to do this , it’s for my chm class

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 nh3 classified as a polar molecule

What is the area in square meters of 448 g ai foil that has a thickness of 23921 nm? the density is 2.70 g/cm