Which of the following materials fall in the category of a "pure substance"?

When a bar magnet is brought closer to a mixture of iron filings and sulphur powder,iron particles stick to the magnet,whereas in the case of iron sulphide,no change is observed. When a mixture of iron and sulphur is added to carbon disulphide,sulphur dissolves,whereas in the case of iron sulphide,no change is observed. Justify the statement that the properties of a compound are different from its constituents,while a mixture shows the properties of its constituent elements using the example of iron and sulphur.

Why is blood a mixture and graphite an element? Mention any one reason for each.

Identify which of the following are elements,mixtures,or compounds:
$(i)$ Brass $(ii)$ Diamond $(iii)$ Sand.

Which of the following are chemical changes?
$(i)$ Decaying of wood
$(ii)$ Burning of wood
$(iii)$ Sawing of wood
$(iv)$ Hammering of a nail into a piece of wood

In nature,carbon is found in elemental forms as: