Is Matter Around us Pure? — Important Questions

They have lustre (shine), They conduct heat and electricity, They are malleable, They are ductile

Metals typically show several characteristic properties: they have lustre (shine), conduct heat and electricity well, are malleable (can be hammered into thin sheets), and are ductile (can be drawn into wires). They are also sonorous (make ringing sounds when hit). Poor conduction of electricity is a property of non-metals, not metals.

Milk, Starch solution, Fog

The Tyndall effect is shown by colloids because their particles are large enough to scatter light. Milk, starch solution, and fog are all colloids. Salt solution and sugar solution are true solutions with very small particles that don't scatter light, so they don't show the Tyndall effect.

Water (H₂O), Carbon dioxide (CO₂), Sodium chloride (NaCl)

Compounds are substances composed of two or more elements chemically combined in fixed proportions. Water (H₂O), carbon dioxide (CO₂), and sodium chloride (NaCl) are all compounds. Iron and oxygen are elements, not compounds, as they consist of only one type of atom.

Evaporation

Evaporation is used to separate salt from salt water because salt has a much higher boiling point than water. When heated, water evaporates leaving behind solid salt crystals. Filtration won't work as salt is dissolved, not suspended. Decantation and magnets are not suitable for this separation.