See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

Concept: The basic strength of an anion is inversely related to the acid strength of its conjugate acid. Stronger the conjugate acid (lower pKa), weaker the base; weaker the conjugate acid (higher pKa), stronger the base. Step 1: Identify the conjugate acids of each anion. - CH3^- (p): conjugate acid is CH4 (methane) - NH2^- (q): conjugate acid is NH3 (ammonia) - OH^- (r): conjugate acid is H2O (water) - F^- (s): conjugate acid is HF (hydrofluoric acid) Step 2: Recall approximate pKa values of the conjugate acids. - CH4: pKa ≈ 48 - NH3: pKa ≈ 38 - H2O: pKa ≈ 15.7 - HF: pKa ≈ 3.2 Step 3: Higher pKa of conjugate acid means the conjugate acid is weaker, which means the anion (base) is stronger. Order of pKa: CH4 (48) > NH3 (38) > H2O (15.7) > HF (3.2) Step 4: Therefore, order of basic strength: CH3^- > NH2^- > OH^- > F^- That is: p > q > r > s Step 5: Why other options fail. - Option (b): q > p > r > s is wrong because CH3^- is a stronger base than NH2^- (pKa of CH4 > pKa of NH3). - Option (c): r > q > p > s is wrong; it places OH^- above NH2^- and CH3^-, which contradicts the pKa ordering. - Option (d): r > p > q > s is wrong for similar reasons, misplacing OH^- at the top. Therefore, the correct answer is A.