Give the uses of alkanes.

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

Knocking sound occurs in an engine when fuel:

Given below are two statements:
Statement $I$ : The boiling point of three isomeric pentanes follows the order
$n$-pentane $>$ isopentane $>$ neopentane
Statement $II$ : When branching increases,the molecule attains a shape of sphere. This results in smaller surface area for contact,due to which the intermolecular forces between the spherical molecules are weak,thereby lowering the boiling point.
In the light of the above statements,choose the most appropriate answer from the options given below:

Complete the following reactions:
$(i)$ $n$-heptane $\xrightarrow[773 \ K, 10-20 \ atm]{Cr_2O_3/V_2O_5/Mo_2O_3}$ ?
(ii) $CH_4 + O_2 \xrightarrow[523 \ K, 100 \ atm]{Cu}$ ?

Briefly explain the trends in boiling point and melting point in the alkane series.