Suggest a suitable separation technique for the following:
$(i)$ Mercury and water.
$(ii)$ Coloured components from blue ink.
$(iii)$ Ammonium chloride and potassium chloride.
$(iv)$ Mixture of alcohol and water.

$A$ 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?

$A$ mixture of sulphur and carbon disulphide is

Two substances,$A$ and $B$,were made to react to form a third substance,$A_2B$,according to the following reaction: $2A + B \to A_2B$. Which of the following statements concerning this reaction are incorrect?
$(i)$ The product $A_2B$ shows the properties of substances $A$ and $B$.
$(ii)$ The product will always have a fixed composition.
$(iii)$ The product so formed cannot be classified as a compound.
$(iv)$ The product so formed is an element.

Answer the following:
$(a)$ Under which category of mixtures will you classify alloys and why?
$(b)$ $A$ solution is always a liquid. Comment.
$(c)$ Can a solution be heterogeneous?

What is tincture of iodine? Identify the solute and solvent in 'tincture of iodine.' Why is the Tyndall effect not seen in a true solution?