# The correct order of increasing acidic nature is?

## $\text{H"_3"O"^+ < "NH"_4^+ < "HF" < "OH"^(-) < "H"_2"O}$ ${\text{NH"_4^+ < "HF" < "H"_3"O"^+ < "H"_2"O" < "OH}}^{-}$ ${\text{OH"^(-) < "H"_2"O" < "NH"_4^+ < "HF" < "H"_3"O}}^{+}$ ${\text{H"_3"O"^+ < "HF" < "H"_2"O" < "NH"_4^+ < "OH}}^{-}$

Apr 8, 2018

3.

#### Explanation:

Acidic nature is determined by a low $p H$.
$p H$ is given by:
$p H = - \log \left[{H}_{3} {O}^{+}\right]$
where $\left[{H}_{3} {O}^{+}\right]$ is the concentration of oxonium ions- so the most acidic species in this bunch must be the oxonium ion-${H}_{3} {O}^{+}$

Conversely, an alkaline character is given by a high $p H$, which implies a high concentration of $O {H}^{-}$ ions- so this must be what has the last acidic character of the listed ions and molecules.

Hence the only appropriate one seems to be option 3.