Which of the following is a weak electrolyte?

The correct answer is option 3. Ethanoic acid.

The weak electrolyte among the options provided is Ethanoic acid.

Ethanoic acid (also known as acetic acid), is a weak electrolyte. When it dissolves in water, it only partially dissociates into ions. Therefore, it conducts electricity to a lesser extent compared to strong electrolytes like sodium chloride or calcium chloride, which completely dissociate into ions when dissolved in water.