Define a solution. Give an example of $(i)$ gas in liquid solution $(ii)$ gas in gas solution.

Calculate the mass of sodium sulphate required to prepare its $20\%$ (mass percent) solution in $100\,g$ of water. (in $,g$)

Define the term $solution$. Identify the solute and solvent in the following solutions:
$(i)$ Tincture of iodine
$(ii)$ Polluted air
$(iii)$ Soda water
$(iv)$ Dilute hydrochloric acid

$A$ group of students took an old shoe box and covered it with black paper from all sides. They fixed a source of light (a torch) at one end of the box by making a hole in it and made another hole on the other side to view the light. They placed a milk sample contained in a beaker/tumbler in the box as shown in the figure. They were amazed to see that the milk taken in the tumbler was illuminated. They tried the same activity by taking a salt solution but found that light simply passed through it.
$(a)$ Explain why the milk sample was illuminated. Name the phenomenon involved.
$(b)$ Same results were not observed with a salt solution. Explain.
$(c)$ Can you suggest two more solutions which would show the same effect as shown by the milk solution?

$(a)$ Both smoke and fog are aerosols. In what way are they different?
$(b)$ How do sol and gel differ from each other? Give one example for each.

What happens when a hot saturated solution is cooled?