Final answer:
The weak electrolyte from the given options is HC₂H₃O₂, commonly known as acetic acid, because it partially dissociates in water, compared to other options which are strong electrolytes.
Step-by-step explanation:
The example of a weak electrolyte from the choices provided is b) HC₂H₃O₂, which is also known as acetic acid. Weak electrolytes partially dissociate in water, creating relatively low concentrations of ions compared to strong electrolytes, which fully dissociate. Strong acids like HNO₃ and ionic compounds such as MgCl₂ and Na₂CO₃, which fully dissociate, are considered strong electrolytes. Therefore, acetic acid (HC₂H₃O₂) is correctly identified as a weak electrolyte as it does not completely ionize in an aqueous solution, unlike HCl which is known to be a strong acid and fully dissociates.