a pure substance means its like a natural substance that has not been tampered with, such as sodium. but when sodium is mixed with chlorine it becomes sodium chloride( table salt), which is a mixture.
A pure substance is a substance which cannot be separated physically or chemically. It is the same wherever found on earth. For example, pure gold is a pure substance. It will be the same whether it is found where you live or on another country. A mixture can be either homogeneous or heterogeneous. A homogeneous mixture is a mixture that looks the same throughout but is made of more than one element. An example of this would be salt and water mixture. A heterogeneous mixture is a mixture in which you can easily identify the different parts which make it up. An example of this would be pizza. Both these mixtures can be broken into different parts either physically or chemically.
