$(a)$ State the difference between a pure substance and a mixture. Give one example of each.
$(b)$ Identify homogeneous mixtures from the following:
$(i)$ Smoke
$(ii)$ Brass
$(iii)$ Tincture of iodine
$(iv)$ Milk

$(II, III)$ Pure substance consists of particles of only one kind of matter. These can be elements or compounds; for example, $Gold$ or $Water$. $A$ mixture is obtained by mixing two or more different elements or compounds which do not react chemically; for example, $Salt$ solution in water.
$(b)$ The homogeneous mixtures are:
$(ii)$ $Brass$ (an alloy of copper and zinc).
$(iii)$ $Tincture$ of iodine (a solution of iodine in alcohol).