Which of the following compounds is the strongest acid?

• A. Hydrochloric acid ($H_{\mathrm{Cl}}$)
• B. Water ($H_{2}O$)
• C. Phenol ($C_6{H}_5\mathrm{OH}$)
• D. Acetic acid (${\mathrm{CH}}_3\mathrm{COOH}$)

Answer: (A)

Verified step by step guidance

1. Understand the concept of acidity: Acidity is determined by the ability of a compound to donate a proton (H+). The stronger the acid, the more readily it donates a proton.
2. Consider the molecular structure and stability of the conjugate base: Strong acids have weak conjugate bases. Evaluate the stability of the conjugate base formed after the acid donates a proton.
3. Evaluate the electronegativity and size of the atoms involved: In general, acids with more electronegative atoms or larger atoms tend to be stronger because they stabilize the negative charge of the conjugate base better.
4. Compare the given compounds: Hydrochloric acid (HCl) is a strong acid because it completely dissociates in water, forming H+ and Cl-. Water (H2O) is neutral, phenol (C6H5OH) is a weak acid, and acetic acid (CH3COOH) is a weak acid.
5. Conclude based on dissociation: Hydrochloric acid (HCl) is the strongest acid among the given options because it fully dissociates in solution, making it a strong acid compared to the others which are weak acids or neutral.