Which of the following materials fall in the category of a "pure substance"?

Salt can be recovered from its solution by evaporation. Suggest some other technique for the same?

$(a)$ Define an element.
$(b)$ Identify non-metals from the following elements: Carbon,Potassium,Silicon,Chlorine,Mercury.

Fill in the blanks:
$(a)$ $A$ colloid is a .......... mixture and its components can be separated by the technique known as .........
$(b)$ Ice,water,and water vapour look different and display different ......... properties but they are ......... the same.
$(c)$ $A$ mixture of chloroform and water taken in a separating funnel is mixed and left undisturbed for some time. The upper layer in the separating funnel will be of ......... and the lower layer will be that of .........
$(d)$ $A$ mixture of two or more miscible liquids,for which the difference in the boiling points is less than $25 \, K$,can be separated by the process called .........
$(e)$ When light is passed through water containing a few drops of milk,it shows a bluish tinge. This is due to the ......... of light by milk and the phenomenon is called ......... . This indicates that milk is a ......... solution.

Why is the path of light not visible in a solution when a beam of light is passed through it?

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