What is the bond length of the $C-C$ bond in an alkane where all carbon atoms are $sp^{3}$ hybridized (in $pm$)?

The decreasing order of boiling points of the following alkanes is:
$(a)$ Heptane
$(b)$ Butane
$(c)$ $2-$methylbutane
$(d)$ $2-$methylpropane
$(e)$ Hexane
Choose the correct answer from the options given below:

Identify the type of reaction shown in the following chemical equation:
$C_6H_5CH_3 + Br_2 \xrightarrow{h\nu} C_6H_5CH_2Br + HBr$

The $C-H$ bond length is longest in which of the following?

$A$ compound $A$ contains $C$ and $H$ only and has a molecular mass of $72$. Its photochlorination gives a mixture containing only one monochloro and two dichloro hydrocarbons. What is its $IUPAC$ name?

$CH_3-CH_2-COO^{-} Na^{+} \xrightarrow[\Delta]{NaOH + ?} CH_3-CH_3 + Na_2CO_3$. Consider the above reaction and identify the missing reagent/chemical.