Name the technique used to separate:
$(i)$ Butter from curd,
$(ii)$ Salt from sea-water,
$(iii)$ Camphor from salt.

Which of the following materials fall in the category of a 'pure substance'?
$(a)$ Ice $(b)$ Milk $(c)$ Iron $(d)$ Hydrochloric acid $(e)$ Calcium oxide
$(f)$ Mercury $(g)$ Brick $(h)$ Wood $(i)$ Air.

Which of the following are chemical changes?
$(a)$ Growth of a plant
$(b)$ Rusting of iron
$(c)$ Mixing of iron filings and sand
$(d)$ Cooking of food
$(e)$ Digestion of food
$(f)$ Freezing of water
$(g)$ Burning of a candle

Classify the following as chemical or physical changes:
$1$. Cutting of trees
$2$. Melting of butter in a pan
$3$. Rusting of almirah
$4$. Boiling of water to form steam
$5$. Passing of electric current through water and the water breaking down into hydrogen and oxygen gases
$6$. Dissolving common salt in water
$7$. Making a fruit salad with raw fruits
$8$. Burning of paper and wood

Try segregating the things around you as pure substances or mixtures.

What is meant by a pure substance?