State any one difference between pure and impure substances.

$(a)$ Write any three points of differences between homogeneous and heterogeneous mixtures.
$(b)$ Give two reasons for supporting that water is a compound and not a mixture.

Smoke and fog both are aerosols. In what way are they different?

Fractional distillation is suitable for the separation of miscible liquids with a boiling point difference of about $25\, K$ or less. What part of the fractional distillation apparatus makes it efficient and provides an advantage over a simple distillation process? Explain using a diagram.

Observe the apparatus shown and answer the following questions:
$(a)$ Name the apparatus.
$(b)$ State one use of the apparatus.
$(c)$ State the principle involved in this process.

How can we obtain different gases from air?