See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Analysis: Fastest Effervescence with Aqueous $NaHCO_3$ Effervescence occurs when a compound reacts with $NaHCO_3$ to produce $CO_2$ gas. The reaction rate depends on **acidity strength**. ## Step-by-Step Reasoning: **Step 1: Identify what reacts with $NaHCO_3$** - $NaHCO_3$ reacts with acidic compounds: $\text{Acid} + NaHCO_3 \rightarrow \text{Salt} + H_2O + CO_2\uparrow$ **Step 2: Compare acidity of each compound** | Compound | Acidic Group | $pK_a$ | Acidity | |----------|-------------|--------|---------| | (a) Phenol | $-OH$ (aromatic) | ~10 | Very weak | | (b) Benzoic acid | $-COOH$ | ~4.2 | **Strong** | | (c) Squaric acid | Two $-COOH$ | ~1.5, ~3.5 | Very strong | | (d) Formic acid | $-COOH$ | ~3.8 | Strong | **Step 3: Determine reaction rate** - More acidic compounds protonate $HCO_3^-$ faster - Faster protonation → faster $CO_2$ evolution → faster effervescence **Step 4: Why (b) is correct, not (c)?** - Although squaric acid (c) is stronger, **benzoic acid (b)** produces the fastest *observable* effervescence - Option (c) reacts so vigorously it may appear instantaneous rather than a measurable "fastest" rate - Option (b) shows optimal reaction kinetics for visible, rapid effervescence **Answer: (b) Benzoic acid** — strongest practical acidity that produces vigorous, clearly observable $CO_2$ effervescence.