What is an ore of iron?

Write true or false for the following statement:
Silver and gold react with oxygen at high temperatures.

How many carats is pure gold?

$(a)$ An ore on heating in air gives sulphur dioxide gas. Name the method in each metallurgical step that will be required to extract this metal from its ore.
$(b)$ State which of the following reactions will take place or not,giving a suitable reason for each.
$Zn(s) + CuSO_4(aq) \rightarrow ZnSO_4(aq) + Cu(s)$
$Fe(s) + ZnSO_4(aq) \rightarrow FeSO_4(aq) + Zn(s)$

What is the chemical formula of alumina?

Which gas is a mixture of carbon monoxide $(CO)$ and dihydrogen $(H_2)$?