Which of the following allotropes of carbon is isomorphous with crystalline silicon?

Among the following elements,$X$ exhibits maximum catenation and $Y$ is the least abundant on earth. $X$ and $Y$ elements are

Observe the following reactions (unbalanced):
$P_2O_3 + H_2O \rightarrow X$
$P_4O_{10} + H_2O \rightarrow Y$
The number of $P=O$ bonds present in $X$ and $Y$ are respectively:

Match the species given in Column-$I$ with the properties mentioned in Column-$II$.

Column-$I$	Column-$II$
$A$. $BF_4^-$	$1$. Oxidation state of central atom is $+4$
$B$. $AlCl_3$	$2$. Strong oxidizing agent
$C$. $SnO$	$3$. Lewis acid
$D$. $PbO_2$	$4$. Can be further oxidized
	$5$. Tetrahedral shape

Identify the cyclic silicate ion given in the figure below:

Thermodynamically,the most stable form of carbon is