purity

Question 1

pure substances

Answer 1

if a substance is pure it is only made of one element or compound
if more than 1 is present it is not pure

Question 2

a mixture

Answer 2

if more than one element present it is now a mixture.
an alloy is a mixture

Question 3

testing for purity

Answer 3

every pure substance has a specific melting/ boiling point
so by comparing the actual melting/boiling point of the sample to the expected value