What does the atomic number of an element refer to? 

• the number of neutrons in an atom

  
  

• the mass number of an atom

  
  

• the number of protons in an atom

  
  

• the atomic mass of an element

  
  

Which term identifies each isotope of an element and is the sum of the number of protons and neutrons in the nucleus? 

• atomic number

  
  

• atomic mass

  
  

• mass number

  
  

• atomic mass unit (amu)

  
  

In a neutral atom, what is the number of electrons equal to?

• mass number 

  
  

• atomic mass 

  
  

• atomic number 

  
  

• neutron number

  
  

Which of the following is true? 

• An atom’s mass depends mainly on the number of electrons it contains.

  
  

• The atomic mass of an element is the weighted average of the atomic numbers of an isotope.

  
  

• A mass of 1 amu is nearly equal to the mass of a single electron.

  
  

• One atomic mass unit (amu) is one-twelfth the mass of a carbon-12 atom.

  
  

Select the two atoms that are isotope of each other