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A colloid in which the dispersion medium is water is known as hydrosol.

In heterogeneous catalysis the reaction always starts at the surface of the catalyst. So, it is also known as surface catalysis.

Critical temperature is the minimum temperature above which a gas cannot be liquefied howsoever high the pressure may be applied.

(a)  Fe°/Pd°

(ii) a → c → b → d → e

The correct answer is (ii) Na₃PO₄

(d) Suiphide ores

 In froth floatation process sulphide ore is shaken with pine oil and water, the ore particles are adsorbed on froth that floats and the gangue particles settle down in tank. Thus, role of adsorption in froth floatation process can be understood as following processes. (i) Adsorption of pine oil on sulphide ore particles. (ii) Formation of emulsion takes place. (iv) Froth is formed along with ore particles. (v) Mechanism of the functioning of shape selective catalysis. As sulphide are extracted using froth floatation method therefore, only sulphide ore particles will show these type of adsorbing tendency.

1. Antibodies such as penicillin and streptomycin are produced in colloidal form for suitable injections. They cure pneumonia. 

2. Colloidal gold and colloidal calcium are used as tonics. 

3. Milk of magnesia is used for stomach troubles. 

4. Silver sol protected by gelatine known as Argyrol is used as eye lotion.

Carbon dust in air is solidified by Cortrell’s precipitator. In it. a high potential difference of about 50.000V is used. The change on carbon is neutralised and solidified. Thus the air is free from carbon particles.

Due to coagulation of colloidal clay particles by electrolytes Present in the sea.

(b) 50,000 V

(a) Ammoniacal AgNO₃

(a) Sky looks blue in colour because colloidal particles suspended in environment scatter the light and blue light is scattered maximum. 

(b) The charged colloidal particles of river water neutralized by ions present in sea water so coagulation take place. 

(c) The charged colloidal particles present in blood are neutralized by ions of alum.

(c) Tyndall effect

Dust particles along with water particles scatter blue light maximum.

(a) Sky looks blue in colour because colloidal particles suspended in environment scatter the light and blue light is scattered maximum. 

(b) The charged colloidal particles of river water is neutralized by ions present in sea water. So coagulation takes place.

(c) The charged colloidal particles present in blood are neutralized by ions of alum. 

At the time of setting, the sun is at the horizon. The light emitted by the sun has to travel a longer distance through the atmosphere. As a result, blue part of the light is scattered away by the dust particles in the atmosphere. Hence, the red part is visible.

Two types of emulsions are as follows : 

Application of Emulsions : 

(i) In medicine: The various pharmaceuticals and cosmetics are available in liquid form such as cod liver oil etc., and some creams and ointment are emulsions of water in oil type. 

(ii) Cleaning action of soap: This action is based on the formation of oil in water type emulsions.

Emulsions are liquid-liquid colloidal systems or the dispersion of one liquid in another liquid.

Type :

(i) Oil dispersed in water (O/W type)

Example: milk and vanishing cream.

(ii) Water dispersed in oil (W/O)

Example: butter and cold cream. 

Liquid -Liquid collidal systems: example-milk

Detailed Answer: 

Emulsions are Liquid-Liquid colloidal systems. 

For example : milk, cream.

Electrophoresis: The movement of colloidal particles towards a particular electrode under the influence of an electric field is called electrophoresis.

Dialysis is a process of removing a dissolved substance from a colloidal solution by means of diffusion through a suitable membrane.

The Brownian movement has a stirring effect, which does not allow the particles to settle.

OR

Brownian movement has a stirring effect which does not permit the particles to settle resulting in the stability of colloidal sols.

Due to presence of equal and similar charges on colloidal particles causing repulsion also results in the stability of colloidal sol.

The stability for colloidal sols is due to Brownian movement and presence of equal i,e., and similar charges which causes repulsion between then and prevents the coagulation of the sol.

The process of making emulsion using a mixture of two immiscible or partially miscible liquids is called emulsification. For example. Cod liver oil is an emulsion made up of water in oil.

Reason for the stability of colloidal sols are:

1. Coagulation of the colloidal sol is prevented because of the presence of equal and similar harges on the colloidal particles.

2. Colloidal particles are covered by a sheath of liquid in which they are extensively solvated because of which they acquire stability.

The two reasons are: 

(i) Due to electron capture by sol particles during electro dispersion of metals, due to preferential adsorption of ions from solution. 

(ii) Dissociation of colloidal sols.

Gold sol. which is lyophobic starts behaving like lyophilic sol. 

Air is not a colloidal solution

(b) to stabilize the colloid and to prevent the crystallization

Copper  is used in  electrical wires and coins.

(a) Reactivity of metal 

(b) Suitable electrodes

(a) Copper is used in making electrical wires because it is ductile and good conductor of electricity. 

(b) Copper is used in making utensils because it is good conductor of heat. 

Copper - BRONZE - COINS

Aluminium - MAGNALUM - PRESSURE COOKER

Iron - STAINLESS STEEL - UTENSILS

Four uses of emulsions:

1. Cleansing action of soaps is based on the formation of emulsions.
2. Digestion of fats in intestines takes place by the process of emulsification.
3. Antiseptics and disinfectants when added to water form emulsions.
4. The process of emulsification if used to make medicines.

(a)  4 3 2 1

(a)  2 4 1 3

(a)  4 3 1 2

Common salt solution. 

It is a true solution whereas others are colloids.

Starch solution. 

It is a suspension whereas others are colloids.

(i) Dispersed phase in smoke : Solid, 

Dispersion medium in smoke: Gas

(ii) In milk, dispersion medium is liquid, the dispersed phase is liquid. Based on the state of dispersed phase, colloid is emulsion.

A colloid in which the dispersion medium is water is known as hydrosol.

Zeolite catalyst or shape selective catalyst:

Zeolites are small porous alumina silicates. Their general formula is M₃ [(Al₂O₃)_x (SiO₂)_y]₃ n H₂O where n is the oxidation state of metal (M).
Example:
Zeolite catalyst ZSM-5 is used in the conversion of alcohol into petrol (gasoline). The dehydration of alcohol takes place on pores of zeolite and forms a mixture of hydrocarbons. 

Due to excessive dialysis, traces of electrolyte which stabilises the colloids is removed completely, making the colloid unstable. As a result coagulation takes place.

The accumulation of molecules species at the surface rather in the bulk of a solid or liquid is termed adsorption.

Chemical adsorption is a process in which gas molecules are held to the surface by formation of chemical bonds.

e.g., Adsorption of O₂ on tungsten, Adsorption of H₂ on nickel.

Adsorption is the odhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. In adsorption, if the concentration of a substance in the interface is high, then it is called positive adsorption. If it is less, then it is called negative adsorption.

The gaseous molecules diffuse on to the surface of the solid catalyst and get adsorbed. After the required chemical changes the products diffuse away from the surface of the catalyst leaving the surface free for more reactant molecules to get adsorbed and undergo reaction.

After the reaction is over between adsorbed reactants, the process of desorption is important to remove products and further create space for the other reactant molecules to approach the surface and react.