In general chemistry: In a neutral aqueous solution at 25°C, which statement best describes the presence of hydrogen ions (H+) and hydroxide ions (OH−)?\n(Assume pure water or a solution whose pH equals 7.0 under standard conditions.)

Introduction / Context:
Neutral solutions are foundational in acid–base chemistry. Understanding what “neutral” means at the ionic level clarifies how pH, autoionisation of water, and electrical neutrality relate. This question checks whether you know that neutrality does not mean the absolute absence of ions; rather, it means equal activities (or concentrations, for introductory purposes) of hydrogen ions and hydroxide ions.

Given Data / Assumptions:

• Temperature is taken as 25°C (standard textbook reference for pH 7 neutrality).
• System is water or a dilute aqueous solution where water autoionisation dominates.
• Ideal behaviour is assumed for simplicity.

Concept / Approach:
Water self-ionises: H2O ⇌ H+ + OH− with ionic product Kw. At 25°C, Kw ≈ 1.0 * 10^-14, so [H+] = [OH−] = 1.0 * 10^-7 mol/L in pure water. “Neutral” therefore means equality of these concentrations, not their absence.

Step-by-Step Solution:

Verification / Alternative check:
pH = −log10[H+] = 7.00; pOH = −log10[OH−] = 7.00; pH + pOH = 14.00, consistent with neutrality at 25°C.

Why Other Options Are Wrong:

• H+ ions are absent: Incorrect; they are present at 10^-7 mol/L.
• OH− ions are absent: Incorrect; they are present at 10^-7 mol/L.
• None of these: Incorrect because one option is exactly correct.

Common Pitfalls:
Confusing “neutral” with “no ions present.” Also, forgetting that pH 7 corresponds to 25°C; at other temperatures, neutral pH shifts because Kw changes.

Final Answer:
Both H+ and OH− ions are present in very small but exactly equal concentrations.