For a protective colloid µ lesser the value of gold number better is the protective power. Thus the correct order of protective power of A,B,C and D is ⇒      ‌‌(A)<(C)<(B)<(D) ‌ Gold number ‌‌0.50‌‌‌0.10‌‌‌0.01‌‌‌‌‌0.005