According to the Arrhenius concept in basic chemistry, how can an acid be defined in terms of the ions it produces in aqueous solution?

Introduction / Context:
Acids and bases are central concepts in chemistry. There are several ways to define acids, including Arrhenius, Bronsted Lowry and Lewis definitions. At the basic level, the Arrhenius concept is often introduced first, because it is simple and applies to aqueous solutions. This question asks you to identify the correct Arrhenius definition of an acid, focusing on the ions produced when the substance dissolves in water.

Given Data / Assumptions:

• We consider aqueous solutions, meaning the solvent is water.
• Arrhenius acids and bases are defined in terms of H⁺ and OH⁻ ions.
• The options mention hydroxide ions, hydrogen ions, taste, electron pairs and solubility.
• We are looking specifically for the Arrhenius definition, not Bronsted or Lewis.

Concept / Approach:
According to Arrhenius, an acid is a substance that increases the concentration of hydrogen ions, H⁺, in aqueous solution, while a base is a substance that increases the concentration of hydroxide ions, OH⁻. This simple definition works well for common acids such as hydrochloric acid and sulphuric acid and bases such as sodium hydroxide. Later definitions broaden the concept, but Arrhenius is sufficient for many introductory problems. The approach is to recall this basic statement and select the option that mentions production of hydrogen ions in water.

Step-by-Step Solution:
Step 1: Recall the Arrhenius definition of an acid: it produces H⁺ ions in aqueous solution. Step 2: Recall the Arrhenius definition of a base: it produces OH⁻ ions in aqueous solution. Step 3: Check option A, which describes substances that produce hydroxide ions; this matches the definition of a base, not an acid. Step 4: Check option B, which states that the substance produces hydrogen ions when dissolved in water; this matches the Arrhenius definition of an acid. Step 5: Conclude that option B is the correct definition of an acid in the Arrhenius sense.

Verification / Alternative check:
Examples of Arrhenius acids support this choice. Hydrochloric acid, HCl, ionises in water to produce H⁺ and Cl⁻. Sulphuric acid, H2SO4, produces 2H⁺ and SO4²⁻ in solution. Nitric acid, HNO3, gives H⁺ and NO3⁻. In each case, the acid increases the concentration of hydrogen ions in water. Textbook definitions of Arrhenius acid and base consistently agree with this description, leaving no doubt about the correct answer.

Why Other Options Are Wrong:
Option A actually defines an Arrhenius base, like NaOH, not an acid. Option C refers to taste and feel, which are general properties sometimes associated with basic solutions, not precise scientific definitions. Option D describes a Lewis base, which donates electron pairs; a Lewis acid accepts electron pairs instead. Option E claims that acids are always insoluble in water, which is clearly false because many common acids are highly soluble. Only option B correctly captures the Arrhenius definition of an acid as a substance that produces H⁺ ions in water.

Common Pitfalls:
Learners often mix up different acid base theories. For example, they might recall that Bronsted acids donate protons and Bronsted bases accept protons, or that Lewis acids accept electron pairs. It is important to pay attention to the specific theory named in the question. In this case, the key phrase is Arrhenius concept, which is strictly about production of H⁺ and OH⁻ in aqueous solution. Keeping the definitions organised by theory can help avoid confusion.

Final Answer:
According to the Arrhenius concept, an acid is A substance that produces hydrogen ions (H⁺) when dissolved in water.