Which chemical element is common to all acidic solutions in basic school chemistry?

Introduction / Context:
In basic chemistry, acids and bases are defined and identified using several properties, including the ions they release in aqueous solution. Exam questions often ask which element is present in all acids, testing understanding of the fundamental definition of an acid.

Given Data / Assumptions:

- The question asks for the element that is common to all acids. - Four common non metallic elements are listed as options. - We assume the usual definition of acids in school level chemistry, especially in aqueous solutions.

Concept / Approach:
According to the Arrhenius concept, an acid is a substance that increases the concentration of hydrogen ions in aqueous solution. In practice, acids contain hydrogen that can be released as hydrogen ions. Examples include hydrochloric acid, nitric acid, sulphuric acid and acetic acid, all of which have hydrogen atoms in their formula. Therefore, hydrogen is the element common to all acids.

Step-by-Step Solution:
Step 1: Recall the basic definition of an acid in school chemistry, which is a substance that releases hydrogen ions when dissolved in water. Step 2: Look at the chemical formulas of common acids such as HCl, HNO3, H2SO4 and CH3COOH. Step 3: Notice that each of these formulas contains hydrogen atoms which provide the hydrogen ions in solution. Step 4: Compare this with the other listed elements nitrogen, oxygen and carbon, which may appear in some acids but are not present in all. Step 5: Conclude that hydrogen is the only element that is common to all acidic solutions as defined in this context.

Verification / Alternative check:
A textbook on basic chemistry defines acids by their ability to release hydrogen ions and backs this up with many examples, all involving hydrogen. Some newer definitions of acids, like the Bronsted Lowry and Lewis theories, generalise the idea further, but at school level and in most exam questions, the presence of hydrogen that can ionise in solution remains the standard reference point, confirming hydrogen as the answer.

Why Other Options Are Wrong:
Nitrogen appears in some acids such as nitric acid, but it is not present in all acids, for example it is absent in hydrochloric acid. Oxygen is present in many oxyacids like sulphuric and nitric acid, but hydrochloric acid does not contain oxygen, so oxygen cannot be common to all acids. Carbon is present in organic acids like acetic acid but is absent in mineral acids like HCl and HNO3.

Common Pitfalls:
Students may be misled by the fact that many strong acids taught in school contain both hydrogen and oxygen, leading them to incorrectly choose oxygen. Another confusion arises from mixing up the concept of oxidising power with acidity. Focusing on the basic definition that acids release hydrogen ions helps avoid such errors.

Final Answer:
The element common to all acids in basic chemistry is Hydrogen.