$A$ is a protecting colloid. The following data is obtained for preventing the coagulation of $10 \text{ mL}$ of gold sol to which $1 \text{ mL}$ of $10\% \text{ NaCl}$ is added. What is the gold number of $A$?

$1$. Expt. No.	$2$. Wt (in mg) of $A$ added to gold sol	$3$. Coagulation
$1$	$40$	Prevented
$2$	$35$	Prevented
$3$	$25$	Not prevented
$4$	$32$	Not prevented
$5$	$33$	Prevented

• A
  $32$
• B
  $33$
• C
  $35$
• D
  $40$