$(a)$ Calculate the mass of potassium chloride required to prepare its $40 \%$ solution in $100 \, g$ of water.
$(b)$ Explain the term solubility and the effect of temperature on it.

(N/A) Let the mass of potassium chloride required be $x \, g$.
The mass of the solution is $(x + 100) \, g$.
Given that the concentration is $40 \%$,we use the formula:
$\text{Concentration} = \frac{\text{Mass of solute}}{\text{Mass of solution}} \times 100$
$40 = \frac{x}{x + 100} \times 100$
$40(x + 100) = 100x$
$40x + 4000 = 100x$
$60x = 4000$
$x = \frac{4000}{60} = 66.67 \, g$
$(b)$ Solubility is defined as the maximum amount of solute that can be dissolved in a given amount of solvent at a specific temperature to form a saturated solution.
Effect of temperature:
$1$. For most solid solutes,solubility increases with an increase in temperature.
$2$. For gaseous solutes,solubility generally decreases with an increase in temperature.