Pure methane can be prepared by(a) Soda lime decarboxylation(b) Kolbe's electrolytic method(c) Wurtz reaction(d) Reduction with H

The preparation of pure methane can be achieved through the following methods:

(a) Soda lime decarboxylation: This method involves the heating of sodium salts of carboxylic acids with soda lime (a mixture of sodium hydroxide and calcium oxide). This results in the decarboxylation (removal of a carboxyl group) of the acid and the production of an alkane. In the case of methane, sodium formate would be used.

(b) Kolbe's electrolytic method: This method involves the electrolysis of an aqueous solution of a salt of a carboxylic acid. However, this method typically results in the formation of higher alkanes and is not suitable for the production of methane.

(c) Wurtz reaction: This reaction involves the coupling of two alkyl halides with sodium in dry ether to form higher alkanes. This method is also not suitable for the production of methane as it requires a minimum of two carbon atoms.

(d) Reduction with H: This could refer to a reduction with hydrogen gas, which can be used to convert carbon monoxide to methane in the presence of a suitable catalyst. This is known as the Fischer-Tropsch process.

Therefore, the most suitable method for the preparation of pure methane from the options given would be soda lime decarboxylation.