Bone black is a form of which element?

$SnCl_2$ acts as a reducing agent because:

The coordination number of $Al$ in the crystalline state of $AlCl_3$ is

Identify $(P)$ and $(Q)$ in the following reaction:
$2 CH_3 Cl + Si$ $\xrightarrow[570 \ K]{\text{Cu powder}} (P)$ $\xrightarrow{H_2 O} (Q)$ $\longrightarrow \text{Straight chain polymer}$

Carbon and silicon both belong to group $14$, but despite the stoichiometric similarity, their dioxides (i.e., carbon dioxide and silicon dioxide) differ in their structures. Comment.

In which of the following oxyacids is an $O$ atom $NOT$ present between two central atoms?