The plague of tin is the:

Consider the following statements:
$(a)$ $R_2SiO$ is the repeating unit of linear silicones.
$(b)$ $RSiCl_3$ on hydrolysis followed by dehydration gives linear silicones.
$(c)$ Silicones can be used as heat insulators.
$(d)$ Silica is soluble in $HF$.
The correct statement$(s)$ is/are:

Who discovered the allotrope of carbon known as fullerene?

Identify the incorrect statements from the following:
$I.$ Tin in $+2$ state acts as a reducing agent,while lead in $+4$ state acts as a strong oxidising agent.
$II.$ Silicon exists as both $[SiF_6]^{2-}$ and $[SiCl_6]^{2-}$ forms.
$III.$ The hybridisation of carbon in fullerene is $sp^3$.
$IV.$ Among $Ge$,$Sn$,and $Pb$,the lowest melting point is for $Sn$.

Which one of the following is correct about the stability of the given ions?

The group $14$ elements $A$ and $B$ have the first ionisation enthalpy values of $708$ and $715 \ kJ \ mol^{-1}$ respectively. These values are the lowest among their group members. The nature of their ions $A^{2+}$ and $B^{4+}$ respectively is: