See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Solution: Effervescence with NaHCO₃ **Effervescence occurs when $CO_2$ gas is rapidly evolved**, which happens when a compound reacts with $NaHCO_3$ to produce $CO_2$. The key principle: **Compounds must be acidic enough to protonate $HCO_3^-$**, converting it to $H_2CO_3$, which decomposes into $CO_2$ and $H_2O$. $$HCO_3^- + HA \rightarrow H_2CO_3 + A^- \rightarrow CO_2↑ + H_2O$$ **Analysis of each option:** **(A) 2,4-Dinitrophenol:** - The two electron-withdrawing $NO_2$ groups significantly decrease electron density on the benzene ring - This makes the $-OH$ group extremely acidic ($pK_a \approx 4$) - ✓ **Strong acid** → reacts with $NaHCO_3$ → **Effervescence occurs** **(B) Salicylic acid derivative (HOOC- and -OH on benzene):** - The carboxylic acid group is highly acidic ($pK_a \approx 2-3$) - ✓ **Strong acid** → **Effervescence occurs** **(C) Acetic acid ($CH_3COOH$):** - Weak organic acid ($pK_a \approx 4.76$), but still acidic enough - ✓ **Reacts with $NaHCO_3$** → **Effervescence occurs** **(D) Benzoic acid ($PhCOOH$):** - Aromatic carboxylic acid ($pK_a \approx 4.2$) - ✓ **Acidic** → **Effervescence occurs** **Answer: All options (A, B, C, D) will give effervescence** because all are sufficiently acidic to protonate bicarbonate ions and produce $CO_2$ gas.