Is it always possible to identify something as an element compound pure substance or mixture

Tooth enamel consists mainly of the mineral calcium hydroxyapatite, ca_10(po_4)_6(oh)_2. trace elements in teeth of archaeological specimens provide anthropologist with clues about diet and diseases of ancient people. students at hamline university measured strontium in enamel from extracted wisdom teeth by atomic absorption spectroscopy. solutions with a constant total volume of 10.0 ml contained 0.726 mg of dissolved tooth enamel plus variable concentrations of added sr. added sr find the concentration of sr in the 10 ml sample solution in parts per billion = ng/ml. find the concentration of sr in tooth enamel in parts per million = mu g/g.

How many moles of potassium are needed to react completely with 12.8 moles of magnessium bromide?

If 15 drops of ethanol from a medicine dropper weigh 0.60g, how many drops does it takes from a dropper to dispense 1.0ml of ethanol? density of ethanol is ethanol is 0.80g/ml.