See image — Practical Organic Chemistry and Purification Chemistry Question

💡 Solution & Explanation

Concept: Vapour density (VD) is defined as the ratio of the mass of a given volume of a gas to the mass of an equal volume of hydrogen under the same conditions. The molar mass (M) of a gas is related to its vapour density by: M = 2 × VD. Step 1: Calculate the molar mass of the gas. M = 2 × VD = 2 × 70 = 140 g/mol Step 2: Determine the molar mass of the formula unit [CO]_x. The molar mass of CO = 12 (C) + 16 (O) = 28 g/mol. Therefore, the molar mass of [CO]_x = 28x g/mol. Step 3: Set the molar mass equal to 140 and solve for x. 28x = 140 x = 140 / 28 x = 5 Step 4: Verify and eliminate other options. - x = 2.5 would give M = 70, not 140. - x = 3.0 would give M = 84, not 140. - x = 6.0 would give M = 168, not 140. Only x = 5.0 gives the correct molar mass of 140 g/mol. Therefore, the correct answer is C.