Which of the following substances is considered basic on the pH scale?

• A. H2O (pure water)
• B. HCl (hydrochloric acid)
• C. CH3COOH (acetic acid)
• D. NaOH (sodium hydroxide)

Answer: (D)

Verified step by step guidance

1. Recall that the pH scale measures the acidity or basicity of a solution, where pH less than 7 is acidic, pH equal to 7 is neutral, and pH greater than 7 is basic (alkaline).
2. Identify the nature of each substance: H2O (pure water) is neutral with a pH of about 7, HCl (hydrochloric acid) is a strong acid with a pH less than 7, CH3COOH (acetic acid) is a weak acid with a pH less than 7, and NaOH (sodium hydroxide) is a strong base with a pH greater than 7.
3. Understand that acids increase the concentration of H\_3O\^+ ions in solution, lowering the pH, while bases increase the concentration of OH\^- ions, raising the pH.
4. Since NaOH dissociates completely in water to produce OH\^- ions, it increases the pH, making the solution basic.
5. Therefore, among the given substances, NaOH is considered basic on the pH scale.