In a typical acid–base neutralisation reaction between an acid and a base, which product is formed along with a salt?

Introduction / Context:
Acid–base reactions are among the most common reactions studied in introductory chemistry. When an acid reacts with a base, they often neutralise each other. Students are expected to know the general form of such reactions and the typical products formed. This question focuses on the classic neutralisation reaction and asks which substance is produced along with a salt when an acid reacts with a base in aqueous solution.

Given Data / Assumptions:

• We are considering standard neutralisation between an acid (providing H+ ions) and a base (providing OH− ions) in water.
• The base may be a hydroxide such as NaOH, KOH, Ca(OH)2, and so on.
• The acid may be hydrochloric acid, sulphuric acid, nitric acid, or other common acids.
• The solution is aqueous, and no redox gas forming reactions are specifically described.

Concept / Approach:
The essential ionic reaction in a simple acid–base neutralisation is: H+ (aq) + OH− (aq) → H2O (l) At the same time, the remaining ions from the acid and base (such as Na+ and Cl−) combine to form a salt that remains dissolved or may crystallise. Therefore, the general products are a salt and water. Hydrogen gas, oxygen gas, carbon dioxide, or chlorine gas may be produced in specific types of reactions, but they are not the standard products of a straightforward acid plus base neutralisation in water.

Step-by-Step Solution:
Step 1: Write a general example, such as HCl (acid) reacting with NaOH (base). Step 2: The molecular equation is HCl + NaOH → NaCl + H2O. Step 3: Identify NaCl as the salt and H2O as the other product. Step 4: Recognise that the net ionic equation highlights formation of water from H+ and OH− ions. Step 5: Conclude that in general, a neutralisation reaction forms a salt and water.

Verification / Alternative check:
Check other examples: sulphuric acid plus sodium hydroxide produces sodium sulphate and water; nitric acid plus potassium hydroxide produces potassium nitrate and water. In every case, the common product besides the salt is water. When acids react with metals or carbonates, gases like hydrogen or carbon dioxide can be released, but those are not simple acid–base neutralisations involving hydroxide bases. This confirms that water is the standard co product with salt in neutralisation reactions.

Why Other Options Are Wrong:
Hydrogen gas is produced when acids react with some active metals, not when they neutralise bases. Oxygen gas may appear in some decomposition or redox reactions, not in typical acid–base neutralisation. Carbon dioxide is produced when acids react with carbonates or bicarbonates, such as Na2CO3 or NaHCO3, but this is a different category of reaction. Chlorine gas might be evolved in certain redox reactions with strong oxidising agents but is not a normal neutralisation product. These options therefore do not match the general acid plus base case.

Common Pitfalls:
Students sometimes mix up gas forming reactions of acids with metals or carbonates and assume that those gases appear in all acid reactions. Another mistake is to focus only on the salt formation and forget that neutralisation also produces water. To avoid confusion, remember that neutralisation means H+ from the acid and OH− from the base combine to form H2O, while the leftover ions form the salt.

Final Answer:
In a typical acid–base neutralisation reaction, the products are a salt and water.