What belongs to the substance and what to the mixture: 1) aluminum 2) sea water 3) iodized salt 4) salt 5) sea sand 6) fuel oil

A substance is called pure if only one type of molecule is found in its sample. The mixture contains molecules of two or more substances.
Pure substances: aluminum (metal), salt (NaCl – sodium chloride or kitchen salt), sea sand (SiO2 – silicon oxide).
Mixtures: sea water (this is a solution of various salts in water), iodized salt (these are sodium chloride and iodine), fuel oil (a mixture of various hydrocarbons with large molecular weights).