Final answer:
A 0.2 mol/l weak acid would typically show the least electrical conductivity because it is a weak electrolyte and has a lower concentration compared to the given base. The correct answer is 0.2 mol/l weak acid.
Step-by-step explanation:
To determine which solution would typically show the least electrical conductivity, one must consider the strength of the electrolytes involved. Electrical conductivity is closely related to the degree of ionization of a substance in solution. Strong acids and strong bases are completely ionized in solution, making them strong electrolytes. In contrast, weak acids and weak bases are only partially ionized in solution, making them weak electrolytes.
Weak acid solutions generally show lower conductivity than strong acid solutions due to their lower degree of ionization. Given the choices, a 0.2 mol/l weak acid would typically show the least electrical conductivity because it is both a weak electrolyte and is present at a lower molarity compared to the 0.3 mol/l weak base.