Question: Two forms of boron are naturally occurring, boron-10 and boron-11. What difference exists between a boron atom with a 10 atomic mass units (amu) and a boron atom with 11 atomic mass units (amu)?

  Options: 
 A. amount of neutrons
 B. number of electrons
 C. size of protons and neutrons
 D. size of electrons and electron cloud 
Answer: A