Arrange the following \(0.10 \mathrm{M}\) solutions in order of increasing acidity: (i) \(\mathrm{HCOONH}_{4}\), (ii) \(\mathrm{NH}_{4} \mathrm{Br}\), (iii) \(\mathrm{NaNO}_{3}\), (iv) \(\mathrm{HCOOK},(\mathrm{v}) \mathrm{KF} .\)

We will analyze each of the given solutions to identify the acidic or basic properties of their cations and anions. (i) \(\mathrm{HCOONH}_{4}\) - The cation is \(\mathrm{NH}_{4}^{+}\) (ammonium ion) which is acidic as it donates proton and the anion is \(\mathrm{HCOO}^{-}\) (formate ion) which is basic as it can accept a proton. (ii) \(\mathrm{NH}_{4} \mathrm{Br}\) - The cation is \(\mathrm{NH}_{4}^{+}\) (ammonium ion) which is acidic and the anion is \(\mathrm{Br}^{-}\) (bromide ion), which is neutral. (iii) \(\mathrm{NaNO}_{3}\) - The cation is \(\mathrm{Na}^{+}\) (sodium ion) which is neutral and the anion is \(\mathrm{NO}_{3}^{-}\) (nitrate ion) which is also neutral. (iv) \(\mathrm{HCOOK}\) - The cation is \(\mathrm{K}^{+}\) (potassium ion) which is neutral and the anion is \(\mathrm{HCOO}^{-}\) (formate ion) which is basic. (v) \(\mathrm{KF}\) - The cation is \(\mathrm{K}^{+}\) (potassium ion) which is neutral and the anion is \(\mathrm{F}^{-}\) (fluoride ion) which is basic.

Below are the acidic and basic properties of the given solutions: (i) \(\mathrm{HCOONH}_{4}\) - Acidic cation and basic anion. (ii) \(\mathrm{NH}_{4} \mathrm{Br}\) - Acidic cation and neutral anion. (iii) \(\mathrm{NaNO}_{3}\) - Neutral cation and neutral anion. (iv) \(\mathrm{HCOOK}\) - Neutral cation and basic anion. (v) \(\mathrm{KF}\) - Neutral cation and basic anion. Now, keeping in mind that acidity is increased by having more acidic cations and decreased by having more basic anions, we can arrange these in order of increasing acidity: Neutral cation and neutral anion: \(\mathrm{NaNO}_{3}\) (iii) Neutral cation and less basic anion: \(\mathrm{HCOOK}\) (iv) Neutral cation and more basic anion: \(\mathrm{KF}\) (v) Acidic cation and less basic anion: \(\mathrm{NH}_{4} \mathrm{Br}\) (ii) Acidic cation and more basic anion: \(\mathrm{HCOONH}_{4}\) (i) So, the order of increasing acidity is (iii) \(\mathrm{NaNO}_{3}\) < (iv) \(\mathrm{HCOOK}\) < (v) \(\mathrm{KF}\) < (ii) \(\mathrm{NH}_{4} \mathrm{Br}\) < (i) \(\mathrm{HCOONH}_{4}\).