When is a compound said to be pure?

Explain why particles of a colloidal solution do not settle down when left undisturbed,while in the case of a suspension they do.

$(a)$ $A$ sugar syrup of mass $214.2\, g$ contains $34.2\, g$ of sugar. Calculate the concentration of sugar in the syrup.
$(b)$ What is a solution?

Name the appropriate methods to separate the following:
$(i)$ Nitrogen from air
$(ii)$ Dye from blue ink
$(iii)$ Butter cream from milk
$(iv)$ Ammonium chloride from common salt

$(i)$ Name the process or the separation technique you would follow to separate:
$(a)$ Dyes in black ink
$(b)$ Butter from cream
$(c)$ Ammonium chloride and common salt
$(d)$ Iron filings and sand
$(ii)$ State the principle used in separation by centrifugation.

Colloids are quite stable. Name the process by which you can separate the components of a colloidal solution.