Gold number of a lyophilic solution is such property that

• Gold number of a lyophilic solution is a such property that the lower its value, the greater is the protecting power. 
• The gold number is defined as the amount of protective colloid which is just sufficient to prevent coagulation of $10\mathrm{ml}$ of a standard hydro gold sol when $1\mathrm{ml}$ of $10\%\mathrm{NaCl}$ solution is added to it. More is the gold number, the less the protective power of the lyophilic solid.

Hence, the correct answer is option C) The lower its value, the greater the protecting power.