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

The treatment of zinc with very dilute nitric acid produces

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

The number of ionisable hydrogens present in the product obtained from a reaction of phosphorus trichloride $(PCl_3)$ and phosphonic acid $(H_3PO_3)$ is

When ferric oxide reacts with $NaOH$,the product formed is

An oxide of an element is a gas and dissolves in water to give an acidic solution. The element belongs to: