As we move from a primary alkane to a tertiary alkane (isomeric alkanes),the boiling point.......

Given below are two statements:
Statement $I$: Methane can be prepared by decarboxylation of sodium ethanoate,Kolbe's electrolysis of sodium acetate and reaction of $CH_3MgBr$ with water.
Statement $II$: Methane cannot be prepared from unsaturated hydrocarbons and by Wurtz reaction.
In the light of the above statements,choose the correct answer from the options given below.

Marsh gas mainly contains .........

Wurtz reaction of methyl iodide yields an organic compound $X$. Which one of the following reactions also yields $X$?

Identify the major product of the following reaction: $CH_3-CH(CH_3)-CH_2-COOH \xrightarrow{NaOH + CaO, \Delta}$

$A$ mixture of two organic chlorine compounds was treated with sodium metal in ether solution. Isobutane was obtained as a product. The two chlorine compounds are