Question

Which of the following is not colloid?
A. Milk
B. Blood
C. Ice-Cream
D. Urea Solution

Answer 1

Hint:In order of the question, to be a colloid, as there will be presence of some microscopically insoluble substances or in other words, a true and pure solution must not be present in a substance. So, we have to check the composition of every optional substance separately.

Complete step-by-step answer: A colloid is a homogeneous non-crystalline mixture consisting of large molecules as one of the substances disperses through the other substance. They include gels, emulsions, sols etc. They cannot be separated by simple filtration or centrifugation. The size of particles range from $1nm\,to\,1\mu m$ . In option A, milk is an emulsion of fat dispersed in water. It has tiny fat particles suspended in the liquid. It can be separated into butter or cream. So, milk is a colloid.In option B, ice cream is also an emulsion of fat dispersed in liquid. It has ice crystals, fat particles dispersed in a mixture of water, sugar and air bubbles. The size of particles range from $20 - 50\mu m$ . So, ice-cream is also a colloidal solution.In option C, blood is a fluid which contains red blood cells, white blood cells and platelets all dissolved in the fluid called plasma. Thus, blood is a colloid.In option D, urea solution contains urea dissolved in water. The solution contains urea as solute and water as solvent and both of them are in the same phase. Thus, urea solution is not a colloid.

Hence, the correct option is (D.) Urea Solution.

Note:Unlike solutions, in which solute and solvent are in the same phase, in colloids both the particles are always in different phases. The particles are always in different phases. The particles are always suspended or take a very long time to settle in the mixture. Colloids can be separated by peptisation or coagulation.