Q.An alcohol (X) gives blue colour in Victor Meyer's test, and 3.7 g of X when treated with metallic sodium liberates 560 mL of hydrogen at 273 K and 1 atm pressure. What is the possible structure of X?

Step 1. Moles of H2 = 560 mL / 22400 mL mol-1 (STP) = 0.025 mol.

Step 2. R-OH + Na gives R-ONa + 1/2 H2, so moles of alcohol = 2 x moles of H2 = 0.05 mol.

Step 3. Molar mass of X = 3.7 g / 0.05 mol = 74 g/mol, which matches C4H10O (a butanol, 4x12 + 10x1 + 16 = 74).

Step 4. Victor Meyer's test gives BLUE colour only for a SECONDARY alcohol (via a nitrolic-acid-forming secondary nitroalkane).

Step 5. Among the C4H10O options, the only SECONDARY alcohol is CH3-CH(OH)-CH2-CH3 (butan-2-ol) -- option (a); option (b) CH3-CH(OH)-CH3 is propan-2-ol, only C3H8O (molar mass 60), and option (d) is a C5 alcohol (molar mass 88), so both fail the molar-mass check.

Back-calculate molar mass from the Na/H2 stoichiometry (R-OH + Na -> R-ONa + 1/2 H2), then use the Victor Meyer colour to fix which structural isomer of that molar mass is correct.

• Ignoring that the printed options don't all share the same molecular formula -- always check molar mass FIRST, then narrow by the Victor Meyer colour.
• Forgetting the 1:2 stoichiometry between alcohol and liberated H2 in the R-OH + Na reaction (each mole of alcohol gives only HALF a mole of H2).