Q23 / 90 · JEE Main 2012 (19 May Online) · Chemistry

On addition of $1 \mathrm{~mL}$ of $10 \% \mathrm{NaCl}$ solution to 10 $\mathrm{mL}$ gold sol in the presence of $0.025 \mathrm{~g}$ of starch, the coagulation is just prevented. Starch has gold number

  • A
    $2.5$
  • Correct answer
    B
    25
  • C
    $0.25$
  • D
    $0.025$

Solution

Gold Number is the minimum amount of lyophilic colloide in miligrams (starch in given case) which prevents the flocculation of $10 \mathrm{ml}$ gold sol by the addition of $1 \mathrm{ml}$ of $10 \% \mathrm{NaCl}$ solution. $\therefore$ Gold number $=$ miligram of starch $=0.025 \times 10^3 \mathrm{mg}$ $=25$

Hence, the correct answer is option: 'B'.

Relevant Questions