See image — Reaction Mechanism Chemistry Question

💡 Solution & Explanation

Step 1: Determine moles of compound (A). Molar mass of C4H10O4 = 4(12) + 10(1) + 4(16) = 48 + 10 + 64 = 122 g/mol. Moles of (A) = 20 / 122 ≈ 0.1639 mol. Step 2: Determine moles of CH4 produced. At STP, 1 mole of gas occupies 22.4 L (old STP definition used in Indian textbook context). Moles of CH4 = 14.6 / 22.4 ≈ 0.6518 mol. Step 3: Determine active hydrogen count per molecule of (A). Grignard reagent (CH3MgBr) reacts with each active hydrogen (OH group) to give one mole of CH4. Moles of CH4 per mole of (A) = 0.6518 / 0.1639 ≈ 3.977 ≈ 4. So compound (A) has 4 active hydrogens, meaning 4 -OH groups. Step 4: Check molecular formula. C4H10O4 with 4 OH groups: 4 oxygens accounted for by 4 OH groups. This is consistent. Step 5: Evaluate each option. Option (a): HOCH2-CH(OH)-CH(OH)-CH2OH (a straight-chain C4 tetraol, e.g., erythritol or threitol). This has 4 -OH groups. Molecular formula: C4H10O4. Correct formula and 4 active H. This is a valid structure. Option (b): HO-CH2-C(OH)(CH2OH)-CH2OH, i.e., a central carbon with one OH and three CH2OH groups (pentaerythritol-like but with only 4 carbons total). Structure: C(CH2OH)3OH where the central C also bears OH — wait, let us count: central C + 3 CH2OH groups = C + 3C = 4 carbons; H count: central C has no H (quaternary), each CH2 has 2H = 6H, each OH contributes 1H = 4H (3 from CH2OH + 1 from central OH) → total H = 6 + 4 = 10; O = 4. Formula = C4H10O4. Correct. Has 4 OH groups → 4 active H. This is also a valid structure. Option (c): 1,2,3,4-cyclobutanetetraol. Molecular formula: C4H8O4 (cyclobutane ring C4H8 minus 4 H + 4 OH = C4H4 + 4OH → C4H8O4). This does NOT match C4H10O4. So option (c) is incorrect. Step 6: Since both (a) and (b) satisfy the molecular formula C4H10O4 and both give 4 moles of CH4 per mole with excess CH3MgBr, both are valid structural formulas for (A). Therefore, the correct answer is D.