Carbon and silicon belong to group $IV$. The maximum coordination number of carbon in commonly occurring compounds is $4$,whereas that of silicon is $6$. This is due to

$(1)$ Half-life of $^{14}C$ is $...........$
$(2)$ $..........$ isotope of carbon is used in radiocarbon dating.
$(3)$ Main component of ceramic,cement and glass is $........$

The stability of dihalides of $Si, Ge, Sn$ and $Pb$ increases in the order:

With respect to graphite and diamond,which of the statement$(s)$ given below is (are) correct?
$(A)$ Graphite is harder than diamond.
$(B)$ Graphite has higher electrical conductivity than diamond.
$(C)$ Graphite has higher thermal conductivity than diamond.
$(D)$ Graphite has higher $C-C$ bond order than diamond.

In the following reaction,identify the nature of the product formed by the complete hydrolysis of the underlined atom at $R.T.$:
$\underline{P}_4O_6 + H_2O \longrightarrow H_3PO_3$

It is observed that $Pb^{2+}$ is more stable than $Pb^{4+}$, while $Sn^{2+}$ is less stable than $Sn^{4+}$. Consider the following reactions:
$PbO_{2} + Pb \rightarrow 2PbO; \Delta_{r}G^{\circ} (1)$
$SnO_{2} + Sn \rightarrow 2SnO; \Delta_{r}G^{\circ} (2)$
Identify the correct set from the following.