Match List-I with List-II.
| List-I (Practice) | List-II (Reason) |
|---|---|
| (A) An alkyl bromide is converted into an alkyl iodide with sodium iodide in dry acetone. | (I) The by-products are gases that escape from the reaction mixture. |
| (B) Thionyl chloride is preferred for converting an alcohol into an alkyl chloride. | (II) The salt formed is insoluble in the solvent, so the forward reaction is favoured. |
| (C) A Grignard reagent is prepared in dry ether. | (III) It is slowly oxidised by air in the presence of light to an extremely poisonous gas. |
| (D) Chloroform is stored in closed dark coloured bottles that are completely filled. | (IV) It reacts with any source of proton, even traces of moisture, to give a hydrocarbon. |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → A-II, B-I, C-IV, D-III
(A) An alkyl bromide is converted into an alkyl iodide with sodium iodide in dry acetone. — This matches (II) The salt formed is insoluble in the solvent, so the forward reaction is favoured. This is the Finkelstein reaction. NaBr does not dissolve in dry acetone and comes out as a solid; removing a product pushes the equilibrium forward (Le Chatelier’s principle).
\( \displaystyle \ce{R-Br + NaI} \xrightarrow{\text{dry acetone}} \ce{R-I + NaBr v} \)
(B) Thionyl chloride is preferred for converting an alcohol into an alkyl chloride. — This matches (I) The by-products are gases that escape from the reaction mixture. SO2 and HCl leave as gases, so the alkyl chloride is left pure.
\( \displaystyle \ce{R-OH + SOCl2 -> R-Cl + SO2 ^ + HCl ^} \)
(C) A Grignard reagent is prepared in dry ether. — This matches (IV) It reacts with any source of proton, even traces of moisture, to give a hydrocarbon. Water, alcohols and amines are acidic enough to destroy RMgX, so even traces of moisture must be kept away.
\( \displaystyle \ce{RMgX + H2O -> RH + Mg(OH)X} \)
(D) Chloroform is stored in closed dark coloured bottles that are completely filled. — This matches (III) It is slowly oxidised by air in the presence of light to an extremely poisonous gas. The gas is phosgene (carbonyl chloride). The dark glass keeps out light, and filling the bottle completely keeps out air.
\( \displaystyle \ce{2CHCl3 + O2} \xrightarrow{\text{light}} \ce{2COCl2 + 2HCl} \)
NCERT (2026-27 edition):
6.4.3 Halogen Exchange – “Alkyl iodides are often prepared by the reaction of alkyl chlorides/ bromides with NaI in dry acetone. This reaction is known as Finkelstein reaction.” … “NaCl or NaBr thus formed is precipitated in dry acetone. It facilitates the forward reaction according to Le Chatelier’s Principle.”
6.4 Methods of Preparation of Haloalkanes – “…Thionyl chloride is preferred because in this reaction alkyl halide is formed along with gases SO2 and HCl. The two gaseous products are escapable, hence, the reaction gives pure alkyl halides.”
6.7.1 Reactions of Haloalkanes – “Grignard reagents are highly reactive and react with any source of proton to give hydrocarbons. Even water, alcohols, amines are sufficiently acidic to convert them to corresponding hydrocarbons.” “It is therefore necessary to avoid even traces of moisture from a Grignard reagent. That is why reaction is carried out in dry ether.”
6.8.2 Trichloromethane (Chloroform) – “…Chloroform is slowly oxidised by air in the presence of light to an extremely poisonous gas, carbonyl chloride, also known as phosgene. It is therefore stored in closed dark coloured bottles completely filled so that air is kept out.”