Separation of Substances-III

Impurities disrupt the regular crystal lattice structure of a pure substance, making it easier to break intermolecular bonds. This melting point depression means impure substances always melt at temperatures lower than their pure form's standard melting point.

Milk is a colloid mixture of water, fats (butterfat), proteins (casein), and sugars (lactose) that cannot be separated by simple filtration. Ice is pure H₂O, iron is a single element, and calcium oxide (CaO) is a pure compound; none are mixtures.

Melting ice is a physical change: only the state changes from solid to liquid while H₂O molecules remain unchanged (reversible). Cooking, butter turning rancid (oxidation), and burning all involve chemical reactions creating new substances with different properties (irreversible).

Distilled water is the purest form of water because it is produced by boiling water into steam and then condensing it back into liquid, leaving behind virtually all impurities, dissolved salts, and contaminants. Sea water contains high salt content, tap water may contain minerals and treatment chemicals, and bottled water like Bisleri undergoes purification but still contains some dissolved minerals compared to completely pure distilled water.

Sulphur in water is a heterogeneous mixture because sulphur is insoluble in water - you can see yellow sulphur particles suspended in water, which will eventually settle at the bottom. The other options form homogeneous mixtures: NaCl dissolves completely in water, iodine dissolves in carbon tetrachloride, and alcohol mixes completely with water to form a uniform solution.

Option (3) is correct.

Option (3) is correct. 

Chalk powder is insoluble in water while salt completely dissolves, so adding water to each substance will clearly differentiate them - the chalk powder will remain as a solid residue at the bottom while salt will disappear into the water. Particle size observation and sieving won't work reliably since both can have similar particle sizes, and heating would just evaporate water from salt but leave both as solids.

Distillation is the correct method because NaCl (salt) has a much higher boiling point than water, so when the solution is heated, water evaporates first and can be collected as distillate, leaving solid salt behind. Sublimation is for solids that directly vaporize, solvent extraction requires another solvent, and liquefaction is converting gas to liquid - none of these separate salt from water effectively.

Filtration specifically separates undissolved solid particles from a liquid - the filter paper allows the liquid to pass through while trapping solid particles. Gases pass through filters, liquids mix with liquids, and 'all of these' would be incorrect because filtration cannot separate gases or miscible liquids.

Sugar and milk forms a homogeneous mixture because sugar completely dissolves in milk, creating a uniform solution where you cannot see separate components or distinguish sugar particles from milk. The other options are heterogeneous: sand in water settles, sugar and sand remain as separate visible particles, and rice in water shows distinct solid particles in liquid.

Salt (NaCl) dissolves fastest in water because it's an ionic compound that readily dissociates into Na+ and Cl- ions when in contact with water. Sugar takes longer to dissolve, baking powder is a mixture that reacts before fully dissolving, and chalk powder is mostly insoluble in water. The ionic nature of salt makes it highly soluble with quick dissolution kinetics.

Evaporation separates sugar from water because when you heat a sugar solution, water (with lower boiling point) evaporates into the air, leaving solid sugar crystals behind. This works because sugar is non-volatile and has a much higher boiling point than water. Cream separation uses centrifugation or churning, alcohol-water separation requires distillation due to closer boiling points, and sand-water would use filtration or sedimentation.

Option (1) is correct.

Option (2) is correct.

Sedimentation is specifically the process where heavy solid particles gradually settle down at the bottom of a liquid due to gravity. Centrifugation uses spinning to force separation, decantation is pouring off liquid after sedimentation, and filtration uses a filter medium - sedimentation is the natural settling process itself.

Common salt (NaCl) is a pure compound, not a mixture, because it has a fixed chemical composition and consistent properties throughout - every part is identical NaCl. Sea water contains salt, minerals, and organic matter (mixture), air is a mixture of nitrogen, oxygen, CO2 and other gases, and pickle contains spices, oil, salt, water and other ingredients (mixture).

Condensation is the process where water vapour (gas) cools down and changes state into liquid water - this is what you see as water droplets on cold surfaces or clouds forming. Evaporation is the reverse (liquid to gas), crystallization is formation of solid crystals from solution, and sublimation is solid directly becoming gas without passing through liquid state.

Mixture of sulphur and sand can be separated through solvent extraction method.  

Curdling is the breaking of an emulsion or colloid into large parts of different composition through the physico-chemical processes of flocculation, creaming and coalescence.