Identify the incorrect statement about $SiO_2$ (silica) from the following.

The $C-C$ bond length is maximum in?

What are allotropes? Sketch the structure of two allotropes of carbon namely diamond and graphite. What is the impact of structure on physical properties of these two allotropes?

Reaction of $NaCl$ with conc. $H_2SO_4$ liberates a gas,$X$ that turns moist blue litmus paper red. When gas $X$ is passed into a test tube containing egg shell powder suspended in water,another gas,$Y$ is generated which when passed through lime water makes it milky. The gases $X$ and $Y$,respectively,are

At high temperature,nitrogen combines with calcium carbide $(CaC_2)$ to give:

Consider the following statements:
$I$. In diamond,each carbon atom is $sp^3$-hybridised.
$II$. Graphite has planar hexagonal layers of carbon atoms.
$III$. Silicones being surrounded by non-polar alkyl groups are water repelling in nature.
$IV$. The order of catenation in group $14$ elements is $Si > C > Sn > Ge > Pb$.
The correct statements are: