The nucleus of an atom contains ____.

The nucleus of an atom contains ____.
 
  a. protons only
  b. electrons only
  c. neutrons only
  d. protons and neutrons
  e. protons and electrons

Question 2

Helium, neon and argon are _____.
 
  a. extremely stable because they have vacancies in their outer shells
  b. extremely stable because they don't have any vacancies in their outer shells
  c. extremely unstable because they have vacancies in their outer shells
  d. extremely unstable because they don't have any vacancies in their outer shells
  e. extremely unstable because they have vacancies in their inner shells