pH 5 corresponds to which type of solution?

• A. Strong acid
• B. Weak acid
• C. Neutral
• D. Weak alkali

Answer: (B)

pH measures how acidic a solution is. A pH of 5 means there are 1 × 10⁻⁵ moles of hydrogen ions per liter, so the solution is acidic but not very strongly so. The distinction between strong and weak acids is about how completely they dissociate in water. Strong acids dissociate fully, so they push the hydrogen ion concentration up a lot, giving very low pH unless the solution is extremely dilute. Weak acids only partly dissociate, so for the same overall concentration they produce fewer H⁺ ions, resulting in a higher pH. That’s why a pH around 5 fits the idea of a weak acid in typical classroom contexts. It isn’t neutral (pH 7) and it isn’t an alkali (pH > 7).