When is a compound said to be pure?

Distinguish between miscible and immiscible liquids. Name the techniques used to separate these liquids.

Fractional distillation is suitable for the separation of miscible liquids with a boiling point difference of about $25\, K$ or less. What part of the fractional distillation apparatus makes it efficient and provides an advantage over a simple distillation process? Explain using a diagram.

What would you observe when
$(a)$ a saturated solution of potassium chloride prepared at $60\,^{\circ}\text{C}$ is allowed to cool to room temperature.
$(b)$ an aqueous sugar solution is heated to dryness.
$(c)$ a mixture of iron filings and sulphur powder is heated strongly.

$(a)$ What is the effect of temperature on the solubility of a solid in a liquid?
$(b)$ Why is it possible to distinguish the particles of solute from those of solvent in a suspension?

Name the process associated with the following:
$(a)$ Dry ice is kept at room temperature and at one atmospheric pressure.
$(b)$ $A$ drop of ink placed on the surface of water contained in a glass spreads throughout the water.
$(c)$ $A$ potassium permanganate crystal is in a beaker and water is poured into the beaker with stirring.
$(d)$ An acetone bottle is left open and the bottle becomes empty.
$(e)$ Milk is churned to separate cream from it.
$(f)$ Settling of sand when a mixture of sand and water is left undisturbed for some time.
$(g)$ $A$ fine beam of light entering through a small hole in a dark room illuminates the particles in its path.