Consider: (a) $FeCl_{3}$ in water - Basic (b) $NH_{4}Cl$ in water - Acidic (c) Ammonium acetate in water - Acidic (d) $Na_{2}CO_{3}$ in water - Basic. Which is/are not correctly matched ?

Question

Accepted Answer

Option 3 is the correct answer because it identifies the pairs that are not correctly matched based on the nature of the solutions formed when these compounds are dissolved in water.

1. **Explanation for Option 3 (Correct Answer):**
   - **(a) $FeCl_{3}$ in water - Basic:** This is incorrectly matched. When $FeCl_{3}$ is dissolved in water, it undergoes hydrolysis to form $Fe(OH)_{3}$ and $HCl$. The formation of hydrochloric acid ($HCl$) makes the solution acidic, not basic.
   - **(c) Ammonium acetate in water - Acidic:** This is also incorrectly matched. Ammonium acetate is a salt formed from a weak acid (acetic acid) and a weak base (ammonium hydroxide). In water, it tends to form a neutral solution because the acidic and basic properties balance each other out. Therefore, it is not acidic.

2. **Explanation for why other options are incorrect:**
   - **Option 1 (b) and (d):**
     - **(b) $NH_{4}Cl$ in water - Acidic:** This is correctly matched. $NH_{4}Cl$ is a salt of a strong acid ($HCl$) and a weak base ($NH_{3}$). In water, it forms an acidic solution due to the presence of $NH_{4}^{+}$ ions, which release $H^{+}$ ions.
     - **(d) $Na_{2}CO_{3}$ in water - Basic:** This is correctly matched. $Na_{2}CO_{3}$ is a salt of a strong base ($NaOH$) and a weak acid ($H_{2}CO_{3}$). In water, it forms a basic solution due to the presence of $CO_{3}^{2-}$ ions, which can accept $H^{+}$ ions.
   
   - **Option 2 (only b):**
     - As explained above, (b) is correctly matched, so this option is incorrect.
   
   - **Option 4 (only d):**
     - As explained above, (d) is correctly matched, so this option is incorrect.

In conclusion, Option 3 is the correct answer because it correctly identifies the mismatched pairs based on the acidic or basic nature of the solutions formed by the given compounds in water.