Question

What is the Arhenius acid that contains the fluoride ion?

Answer 1

Hint: Arhenius theory is a theory of acid and bases. According to this theory, an acid gives a proton, which is a hydrogen ion in any solution. The proton liberated by acids has a tendency to associate with water molecules when dissolved in water to form a hydronium ion. While bases impart or give hydroxide, OH ions in any solutions upon their dissociations.

Complete answer:
Arrhenius acid theory suggests that acids are the species that liberate hydrogen ions, ${{H}^{+}}$ when dissolved in any solution. So, according to this theory the Arhenius acid with fluoride ion would contain a hydrogen ion.
As we know fluoride acts as an anion, it has a valency of -1, as it needs only one electron to complete its noble gas configuration. So, the fluoride anion will need only one cation, therefore, only one hydrogen ion. As hydrogen ion has only one electron in its valence shell which will be taken up by fluoride anion to form the Arhenius acid.
Thus, the acid will be HF, called hydrogen fluoride. The dissociation of HF in water will be:
$HF+{{H}_{2}}O\to {{H}_{3}}{{O}^{+}}+{{F}^{-}}$
The hydrogen ion will associate with the water molecule to form a hydronium ion, ${{H}_{3}}{{O}^{+}}$. This is also the property of acids as they liberate hydrogen ions.
Hence, Arhenius acid that has fluoride ion is HF, hydrogen fluoride acid.

Note:
The Arhenius theory has limitations, as all acids do not contain hydrogen ions, and also all bases do not contain hydroxide ions. For example, $S{{O}_{2}},S{{O}_{3}},N{{O}_{3}}$ are acids but they do not have hydrogen ions. While, $N{{H}_{3}},CaO,N{{a}_{2}}C{{O}_{3}}$ are bases without OH ions. Their reactions with water do, liberate hydrogen and hydroxide ions respectively.