Most liquids that are able to conduct electricity are actually solutions of acids, bases and which of the following?

Introduction / Context:
In basic electricity and chemistry, students learn that pure water is a very poor conductor of electricity, yet many everyday liquids, such as salt solutions and acid solutions, conduct electricity quite well. This behaviour is related to the presence of ions in solution. The question asks which additional category of substances, along with acids and bases, typically forms solutions that conduct electricity. Identifying this category requires linking electrochemistry concepts with common examples from daily life.

Given Data / Assumptions:
- The question focuses on liquids that conduct electricity, usually through ionic conduction in solution.
- It states that such liquids are commonly solutions of acids and bases, and asks for a third type of solute that also forms conducting solutions.
- Four options are provided: salts, copper, aluminium, and iron.
- We assume standard school level definitions of acids, bases, and salts and consider aqueous solutions at room conditions.

Concept / Approach:
Electrical conductivity in liquids often arises from the mobility of ions. Acids produce hydrogen ions in water, bases produce hydroxide ions, and salts dissociate into positive and negative ions. All these ions can move under an applied potential difference, carrying charge and creating an electric current. Metals such as copper, aluminium, and iron conduct electricity in the solid state by electron movement, not by forming solutions in the way referred to here. Therefore, the missing group alongside acids and bases must be salts, which form ionic solutions known as electrolytes.

Step-by-Step Solution:
Step 1: Recall that in aqueous solution, acids ionise to generate hydrogen ions and bases ionise to generate hydroxide ions. Step 2: Recognise that salts are ionic compounds composed of positive and negative ions, such as sodium chloride, potassium nitrate, and calcium chloride. Step 3: When salts dissolve in water, they dissociate into their constituent ions, which can move freely and therefore conduct electric current. Step 4: Consider the alternatives: copper, aluminium, and iron are metals, which conduct electricity in solid form but are not typically referred to as conducting liquids when dissolved. Step 5: Conclude that the group that correctly completes the statement is salts, making solutions of acids, bases, and salts the main liquid conductors of electricity.

Verification / Alternative check:
Practical laboratory experiments reinforce this conclusion. When a bulb is connected in series with electrodes dipped into pure distilled water, the bulb barely glows, indicating poor conductivity. However, if common salt, hydrochloric acid, or sodium hydroxide is added, the bulb glows brightly because these substances produce ions in solution. Science textbooks describe such liquids as electrolytes and specifically list acids, bases, and salts as sources of conducting solutions. Metals such as copper, aluminium, and iron are discussed separately as conductors in solid state, not as solutes responsible for electrolytic conduction. This experimental evidence supports salts as the correct answer.

Why Other Options Are Wrong:
Copper: A good conductor in solid form but not a typical solute mentioned in the context of conducting solutions of acids, bases, and salts.
Aluminium: Again a metallic conductor, but not the intended category of dissolved substances giving rise to conducting liquids.
Iron: A solid conductor that may corrode in solutions, but the question is about solutes forming electrolytes, which is not best described by iron as a category.

Common Pitfalls:
Students sometimes confuse electrical conduction in solids, where electrons move through metallic lattices, with conduction in liquids, where ions are responsible for current. Because copper and aluminium are famous conductors in household wiring, some learners may be tempted to pick these metals. To avoid this error, always note whether the question is about solid conductors or conducting solutions. When the context clearly refers to liquids in which substances are dissolved, think of acids, bases, and salts as the classical electrolyte categories.

Final Answer:
Most liquids that conduct electricity are solutions of acids, bases, and Salts, because salts also dissociate into ions that carry electric current in aqueous solution.