amount of neutrons number of electrons size of protons and neutrons size of electrons and electron cloud
I am hesitating between 4 options to answer the following question, which option should I choose?
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)?
Possibilities:
- amount of neutrons
- number of electrons
- size of protons and neutrons
- size of electrons and electron cloud

amount of neutrons