Which one of the following statements about acids in aqueous solution is incorrect?

Introduction / Context:
Acids are a fundamental class of compounds in chemistry, and their properties are studied early in school curricula. Questions that list several statements about acids and ask which one is incorrect help reinforce a clear understanding of these properties. This question focuses on acids in aqueous solution and includes statements about ion formation, hydrogen content, litmus behaviour, and electrical conductivity. Identifying the incorrect statement requires knowledge of how acids behave when dissolved in water.

Given Data / Assumptions:
- The discussion is about acids in aqueous solution, that is, acids dissolved in water.
- Four statements describe typical properties of acids: ionisation, composition, effect on litmus, and electrical conductivity.
- Only one statement is incorrect and must be identified.
- Standard Arrhenius theory of acids and basic properties of acid solutions are assumed.

Concept / Approach:
According to the Arrhenius concept, acids are substances that produce hydrogen ions in aqueous solution. Many common acids indeed contain hydrogen in their formulas, such as hydrochloric acid and sulphuric acid. Acids turn blue litmus paper red, which is a standard laboratory test. As for conductivity, aqueous solutions of acids contain ions and therefore conduct electricity well, especially when the acid is strong. Thus, any statement claiming that acids are bad conductors of electricity in aqueous solution contradicts this understanding and must be the incorrect one. The other statements correctly describe known properties of acids in water.

Step-by-Step Solution:
Step 1: Evaluate the statement that acids give hydrogen ions in aqueous solution. This matches the Arrhenius definition and is correct. Step 2: Evaluate the statement that most acids contain hydrogen. Common acids such as hydrochloric, nitric, acetic, and sulphuric acids all contain hydrogen, so this statement is broadly correct at basic level. Step 3: Evaluate the statement that acids turn blue litmus red. This is a standard indicator test and is accurate. Step 4: Evaluate the statement that acids are bad conductors of electricity in aqueous solution. In fact, acid solutions are usually good conductors because they contain mobile ions. Step 5: Conclude that the statement about poor electrical conductivity is incorrect and should be selected as the answer.

Verification / Alternative check:
Simple experiments in school laboratories use an electric circuit with a bulb or LED to test conductivity of solutions. Distilled water shows almost no conduction, while dilute hydrochloric acid or sulphuric acid makes the bulb glow brightly, demonstrating good conductivity. Textbooks describe acid solutions as electrolytes that allow electric current to pass. They also emphasise that blue litmus turns red in acidic solutions and that acids contain hydrogen atoms that ionise in water. These multiple sources of evidence confirm that only the statement about acids being bad conductors in aqueous solution is wrong.

Why Other Options Are Wrong (as answers):
They give H+ ions in aqueous solution: This is correct and is part of the definition of acids in the Arrhenius model.
Most acids contain hydrogen in their molecules: This is correct for common acids such as hydrochloric, nitric, acetic, and sulphuric acids at the school level.
They turn blue litmus paper red: This is also correct, reflecting a standard property of acids in indicator tests.

Common Pitfalls:
Learners sometimes assume that only strong acids conduct electricity well and that weak acids do not conduct at all, leading them to incorrectly accept the statement that acids are bad conductors. In reality, even weak acid solutions conduct electricity, though not as strongly as solutions of strong acids. Another pitfall is to over analyse unusual acids at higher levels and question the statement that most acids contain hydrogen. In the context of general school science, that statement is intended to be correct. Always pay attention to the basic level at which the question is framed.

Final Answer:
The incorrect statement is They are bad conductors of electricity in aqueous solution, because acid solutions actually conduct electricity well due to the presence of ions.