Every liquid has a characteristic boiling point at 1 atmospheric pressure. If the given colourless liquid boils at exactly 373K at 1 atmospheric pressure, then it is pure water if the boiling point is even slightly above 373K, then contaminated.

1. There are 22 non-metals:
2. 10 non-metals are solid. Important solid non-metals are carbon, silicon, phosphorus, arsenic, sulphur, and iodine.
3. 11 nonmetals are gases. Some of these are hydrogen, nitrogen, oxygen, fluorine, chlorine,1 non-metals is liquid. For example, bromine.

Brass is a mixture because:
(i) Different samples of brass may have variable compositions.
(ii) Different constituents of brass may have variable compositions.
(iii) The properties of brass depending on the percentage of each pure substance in it.

Yes, all types of changes involve energy during a change, energy is either evolved or absorbed burning of a candle is a chemical change, and energy is evolved. The evaporation of the liquid is a physical change and energy is absorbed.

Mixture of common salt, camphor and iron fillings:
(i) magnet is passed over the mixture several times. Iron fillings attached to one magnet and are separated.
(ii) Camphor is separated from the salt by sublimation. camphor is coollected as sublimate and commonj sali is separated as rsidue.

Crystallization is a process that separates a pure solid in the form of its crystals from a solution. Crystallization is better than evaporation because
(i) In evaporation, some solids may decompose on heating.
(ii) Evaporation can be used with completely non-volatile solids.
(iii) Some impurities may go with the filtrate, which on evaporation would contaminate the solid.

(i) Simple distillation cannot be used if the boiling point difference between the liquids is less than 20-25⁰ C
(ii) Simple distillation cannot be used if it is a mixture of more than two liquids.

Application of crystallisation:
(i) Purification of impure substances.
(ii) Recovery of salt from sea water.

(a) By use of separating funnel. 
(b) No. Water and alcohol when mixed from a single layer and thus separating funnel cannot be used to separate alcohol dissolved in water.

(a) If at given temperature, more salt is added to water, it settles down then it is saturated solution. If on adding more salt, a clear solution is obtained, then the given solution is unsaturated.
(b) We can increase the solubility of saturated solution by raising temperature.

True solution obtained in water are aqueous soliution, e.g., vinegar. true solutions in organic liquids like alcohol, acetone, etc. are non-aqueous solution, e.g., amino acids dissolved in acetone etc.

Take water in a beaker. Heat the water gently to 50⁰ C and slowly add copper sulphate powder, stirring the solution continuously with the help of a glass rod. Continue adding the compound, keeping the temperature of solution at 50⁰ C, till some compound remains undissolved and settle down. Then quickly filter the solution. The solution so obtained is a saturated solution of copper sulphate at 50⁰ C.On cooling, the solubility of copper sulphate will decrease e and it will start settling down at the bottom of the beaker.

Water is a compound because:
(i) The composition of hydrogen and oxygen in water taken from any source is the same.
(ii) The properties of water are different from that of its constituents, i.e., H₂ or O₂.

A pure substance always has the same colour, taste or texture at a given temperature and pressure. Also it has fixed point or boiling point at constant pressure. Also it has a fixed melting point or boiling point at constant pressure. For example, pure water boils at 373k at 1 atmospheric pressure. But water containing some invisible dissolved substance boils at a temperature above 373k.