(a) (i) centrifugation        
(ii) filtration
(iii) Separating funnel      
(iv) Evaporation
(v) Sublimation              
(vi) Winnowing
(b) (i) Physical change    
(ii) Chemical change
(iii) Chemical change      
(iv) Physical change.

Advantages of crystallisation:
(i) Fine crystals of the substance are obtained
(ii) Solids which decompose on heating can be safely purified.
Disadvantages of crystallisation:
(i) Some substance remains with the liquid/ solvent.
(ii) liquid needs to be purified for further use.

(i) True Solution. A true solution is defined as a homogeneous mixture of two or more substances. The term homogeneous means that every portion of the solution has the same properties, e.g., sugar dissolved in water, iodine in ethyl alcohol (tincture).
(ii) Solute. The substance(s) present in smaller proportions in a solution is called the solute.
(iii) Solvent. The substance present in a larger in large proportion in a solution is called the solvent. If a homogeneous mixture or a solution is formed by dissolving 2 g salt in 100 g water, then salt is the solute and water is the solvent.
(iv) Solubility. The maximum amount of the solid that can be dissolved in a given amount of the solvent (water) is termed its solubility at that temperature.

(i) Starch solution and Milk:
These are the colloidal solutions because the particle size is large enough to scatter a beam of light passed through these.
(ii) Soap solution.

Alloy are considered as homogeneous mixture because.
(i) the considered as homogeneous mixtures because
(ii) it shows the properties of its constituent and can have variable composition of its constituents.

Comparison of properties of true solution, colloidal solution, and suspension

Test of a colloidal solution or a suspension.
(i) A colloidal solution is turbid and the particle settles down on adding salt. In a suspension, particles settle down on keeping under the influences of gravity.
(ii) If the particles in a heterogeneous and opaque solution can be seen with naked eyes and get settled on keeping, then it is a suspension.

Mass of silver (Ag) ornament = mg
Mass of gold used for polishing = \(\frac{1}{100}\times\) mg = 0.01 mg
Atomic mass of Ag = 108 u
\(\therefore\) 1 mole of Ag = 108 g = 6.022 x 10²³ atoms
Thus, 108 g of Ag have atoms = 6.022 x 10²³
\(\therefore\) mg of Ag have atoms = \(\frac{6.022\times 10^{23}}{108}\)
Similarly, atomic mass of gold (Au) = 197 u
1 mole of Au = 197 g = 6.022 x 10²³ atoms
Thus, 197 g of Au have atoms = 6.022 x 10²³
\(\therefore\) 0.01 mg of Au will have atoms = \(\frac{6.022\times 10^{23}\times 0.01\ m}{197}\)
\(\therefore\) Ratio of the number of atoms of gold and silver = \(\frac{6.022\times 10^{23}}{197}\times 0.01\ m; \frac{6.022\times 10^{23}}{108}m\)
= \(\frac{1}{19700}:\frac{1}{108}\) 
= 108: 19700