The number of elements present in the fourth period is

The formula of the product formed when sodium thiosulphate solution is added to silver bromide is:

Identify the incorrect statements from the following.
$I$. Tin in $+2$ state acts as reducing agent while lead in $+4$ state acts as strong oxidising agent.
$II$. Silicon exists as $[SiF_6]^{2-}$ form,but $[SiCl_6]^{2-}$ does not.
$III$. The hybridisation of carbon in fullerene is $sp^3$.
$IV$. Among $Ge, Sn$ and $Pb$,the lowest melting point is for $Sn$.

Match the items in Column-$I$ with those in Column-$II$:

Column-$I$	Column-$II$
$A$. Tapetum	$i$. Degenerate during development
$B$. Intine	$ii$. Resistant organic materials
$C$. Vegetative cell	$iii$. Pollen tube
$D$. Sporopollenin	$iv$. Provide nourishment to pollen grains

The oxidation number of $C$ in $HNC$ is .......