See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

**Step 1: Understand nucleophilicity in aqueous medium** Nucleophilicity depends on electron density and basicity. In aqueous solution, nucleophilicity is primarily determined by basicity (ability to donate electron pairs), but solvation effects are crucial—more basic species are better solvated by water, reducing their effective nucleophilicity. **Step 2: Compare basicity order** Basicity order: $OH^- > F^- > HS^- > NH_2^-$ This follows from conjugate acid strength: - $H_2O$ (weakest acid, $pK_a \approx 15.7$) - $HF$ ($pK_a \approx 3.2$) - $H_2S$ ($pK_a \approx 7$) - $NH_3$ ($pK_a \approx 9.2$) **Step 3: Account for solvation in aqueous medium** $OH^-$ and $F^-$ are highly basic and become heavily solvated by water through hydrogen bonding: - $OH^-$ forms strong H-bonds with $H_2O$ - $F^-$ (smallest, highest charge density) is **most heavily solvated** This solvation shell reduces their nucleophilicity significantly. **Step 4: Evaluate fluoride ion** $F^-$ is the smallest anion with highest charge density, making it extremely hydrated. However, among the given options, **$F^-$ shows the best balance**: it's basic enough to be a strong nucleophile, yet its solvation effects are overcome in nucleophilic attack scenarios due to its high reactivity. **Answer: (C) $F^-$** is the strongest nucleophile because, despite heavy solvation, its small size and high electron density make it the most reactive nucleophile in aqueous medium for typical $S_N2$ reactions.