Gold number is defined as:

• A
  The number of $mg$ of lyophilic colloid which should be added to $10 \, mL$ of ferric hydroxide sol so as to prevent its coagulation by the addition of $1 \, mL$ of $10 \, \% \, NaCl$ solution.
• B
  The number of $mg$ of lyophilic colloid which should be added to $10 \, mL$ of standard gold sol so as to prevent its coagulation by the addition of $1 \, mL$ of $10 \, \% \, NaCl$ solution.
• C
  The $mg$ of gold salt to be added to a lyophilic colloid to coagulate it.
• D
  The $mg$ of an electrolyte required to coagulate a colloid.