Write your observations when the following processes take place:
$(a)$ An aqueous solution of sugar is heated to dryness.
$(b)$ $A$ saturated solution of potassium chloride prepared at $60^\circ C$ is allowed to cool at room temperature.
$(c)$ $A$ mixture of iron filings and sulphur powder is heated strongly.
$(d)$ $A$ beam of light is passed through a colloidal solution.
$(e)$ $Dil. HCl$ is added to the mixture of iron and sulphur.

$(a)$ The water evaporates, and sugar remains as a solid residue.
$(b)$ The solubility of potassium chloride decreases with temperature, causing crystals of potassium chloride to form.
$(c)$ Iron reacts with sulphur to form a new compound, iron$(II)$ sulphide $(FeS)$, which is a black-coloured solid.
$(d)$ The path of the light becomes visible due to the scattering of light by colloidal particles, known as the Tyndall effect.
$(e)$ $A$ colourless gas, hydrogen sulphide $(H_2S)$, is evolved, which has a characteristic smell of rotten eggs.