# $10^{-4}\;g$ of gelatin is required to be added to $\;100\;cm^{3}$ of a standard gold sol to just prevent its coagulation by the addition of $\;1\;cm^{3}$ of $\;10\%\;$ NaCl solution to it . Hence , the gold number of gelatin is
$(a)\;10\qquad(b)\;1.0\qquad(c)\;0.1\qquad(d)\;0.01$