What does the $Gold \ Number$ measure?

• A
  It indicates the amount of gold present in a colloidal solution.
• B
  It indicates the amount of gold required to break a colloid.
• C
  It is the minimum amount of protective colloid in milligrams required to prevent the coagulation of $10 \ mL$ of a gold sol when $1 \ mL$ of $10\% \ NaCl$ solution is added.
• D
  None of the above.