Which of the following methods can be used for the preparation of methane?

Which one gives only one monosubstitution product on chlorination?

The cycloalkane formed when $1,4$-dibromopentane is heated with sodium is:

In the reaction of $1$-bromo-$3$-chlorocyclobutane with two equivalents of sodium in ether,the major product is

Octane number has $0$ value for

In the alkane $CH_3-CH_2-C(CH_3)_2-CH_2-CH(CH_3)_2$,identify $1^{\circ}$,$2^{\circ}$,and $3^{\circ}$ carbon atoms and give the number of $H$ atoms bonded to each one of these.