Which one of the following is a weak acid?

The correct option is D

Hydrogen fluoride

The explanation for the correct option

(D) Hydrogen fluoride

Acid

• Acids, according to Arrhenius's theory, are species that dissociate in water to produce hydrogen ions, ${\mathrm{H}}^{+}$.
• However, there are two types of acids found in nature: weak acid and strong acid.
• Weak acids are those that do not completely dissociate in an aqueous solution.
• Strong acids are those that dissociate entirely and readily when dissolved in an aqueous solution.

Hydrogen fluoride

• Hydrofluoric acid $\left(\mathrm{HF}\right)$ is the only weak acid generated by hydrogen and a halogen.
• In water, weak acids do not entirely dissociate into their ions.
• In water, $\mathrm{HF}$ dissociates into ${\mathrm{H}}^{+}$ and ${\mathrm{F}}^{-}$ ions.
• The reaction is as follows:

$\mathrm{HF}\left(\mathrm{aq}\right)\to {\mathrm{H}}^{+}\left(\mathrm{aq}\right)+{\mathrm{F}}^{-}\left(\mathrm{aq}\right)$

The explanation for incorrect options

• Hydrofluoric acid is a weak acid.
• Hence, all other options (A), (B), and (C) are incorrect.

Therefore, the correct option is (D) Hydrogen fluoride.