See image — Hydrocarbons Chemistry Question

💡 Solution & Explanation

Concept: Methane (CH4) is the simplest alkane, and preparing it in pure form requires a method that reliably and exclusively yields CH4 without mixtures of higher alkanes. Step 1 - Soda-lime decarboxylation (option C): When sodium acetate (CH3COONa) is heated with soda-lime (NaOH/CaO), the reaction is: CH3COONa + NaOH → CH4 + Na2CO3. This reaction produces pure methane because the starting material (sodium acetate) gives only a one-carbon product. The method is straightforward and selective. Step 2 - Why Wurtz reaction (option A) fails for pure methane: The Wurtz reaction involves treating an alkyl halide with sodium metal. To get methane, one would use CH3X + 2Na → CH4 + NaX in principle, but in practice the Wurtz reaction on a single type of alkyl halide gives mixtures and is not suitable for methane preparation; it works best for symmetrical higher alkanes. Step 3 - Why Kolbe electrolysis (option B) fails for pure methane: Kolbe electrolysis of acetate gives ethane (CH3COO- → CH3• → C2H6), not methane. Electrolysis of formate would give CO2, not methane. Step 4 - Why reduction with H2 (option D) is not ideal: Reduction of carbon or CO with H2 can give methane but the process yields impure product and is not a standard lab preparation of pure methane. Conclusion: Soda-lime decarboxylation of sodium acetate is the standard, clean laboratory method to obtain pure methane. Therefore, the correct answer is C.