Answer:
You could use a conductivity tester to test conductivities of the solutions.
Step-by-step explanation:
The light bulb (see image below) will glow brightly in a solution of a strong electrolyte like KCl, because there will be many ions available to carry the current.
A solution of a weak electrolyte like acetic acid will contain relatively few ions, so the light bulb will glow weakly.