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

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

State the separation technique you would apply for the separation of the following:
$(a)$ Sodium chloride from its solution in water
$(b)$ Tea leaves from tea
$(c)$ Iron pins from sand
$(d)$ Different pigments from an extract of leaves
$(e)$ Butter from curd
$(f)$ Fine mud particles suspended in water.

How will you separate a mixture of naphthalene powder and common salt? Draw a neat and labelled diagram to show the process.

Identify the solute and the solvent for the following mixtures:
$(a)$ Tincture of iodine
$(b)$ Soda water
$(c)$ Sugar solution
$(d)$ Polluted air
$(e)$ Dilute hydrochloric acid

Salt can be recovered from its solution by evaporation. Can you suggest any other technique also?