What makes an aqueous solution acidic?
AMore hydronium than hydroxide ions
BMore hydroxide than hydronium ions
CEqual hydronium and hydroxide ions
DAn absence of hydroxide ions entirely
Answer & Solution
Correct answer: A. More hydronium than hydroxide ions
1. Both ions are always present, so acidity is a comparison, not a presence test.
2. A solution is acidic when hydronium ions outnumber hydroxide ions.
3. The two concentrations are inversely related through the ion product of water.
4. So raising one necessarily lowers the other.
_Source: OpenStax Chemistry (CC BY 4.0), Ch 14 "Acid-Base Equilibria", section 14.2 pH and pOH_
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