The $C-C$ bond length is maximum in?

Consider the following statements:
Statement-$I$: $CCl_4$ does not undergo hydrolysis,but $SiCl_4$ undergoes hydrolysis.
Statement-$II$: Thermal and chemical stability of $GeX_4$ is more than $GeX_2$.
The correct answer is:

Assertion $(A)$: The maximum covalency of $Si$ and $Ge$ is $6$ but that of carbon is $4$.
Reason $(R)$: Due to the presence of $d$-orbitals in $Si$ and $Ge$,both these elements can undergo $sp^3d^2$ hybridisation and covalency of $6$ is possible. Carbon has no $d$-orbitals in it and hence its covalency is $4$.
The correct answer is:

In the following reaction,identify the nature of the product formed by the complete hydrolysis of the underlined atom at $R.T.$:
$\underline{S}O_3 + H_2O \longrightarrow H_2SO_4$

Which of the following properties is $NOT$ exhibited by carbon?

Which of the following is a good conductor of heat and electricity?