Mention the starting material to produce silicones.

Which of the following is an incorrect statement?

Number of oxygen atoms present in the chemical formula of fuming sulphuric acid is . . . . .

$Si_3O_9^{-6}$ (having three tetrahedral units) is represented as:

Evaluate the following statements related to group $14$ elements for their correctness.
$(A)$ Covalent radius decreases down the group from $C$ to $Pb$ in a regular manner.
$(B)$ Electronegativity decreases from $C$ to $Pb$ down the group gradually.
$(C)$ Maximum covalence of $C$ is $4$ whereas other elements can expand their covalence due to presence of $d$ orbitals.
$(D)$ Heavier elements do not form $p\pi-p\pi$ bonds.
$(E)$ Carbon can exhibit negative oxidation states.
Choose the correct answer from the options given below:

Explain the following:
$(a)$ $CO_2$ is a gas whereas $SiO_2$ is a solid.
$(b)$ Silicon forms $SiF_6^{2-}$ ion whereas corresponding fluoro compound of carbon is not known.