Which of the following is an amphoteric oxide?

$NaHSO_3$ is heated to produce $H_2O$ and compound $'A'$. Which of the following statements is $INCORRECT$ about $'A'$?

$A$ red solid is insoluble in water,but it becomes soluble if a small amount of $KI$ is added to the water. If this red solid is heated in a test tube,it produces a violet-colored vapor and some metallic droplets are observed on the cooler parts of the test tube. This red solid is........

In the following reaction,identify the nature of the product formed by the complete hydrolysis of the underlined atom at $R.T.$:
$\underline{Si}Cl_4 + H_2O \longrightarrow H_4SiO_4 + HCl$

The gas produced by the passage of air over hot coke is

An inorganic compound $(A)$ made of the two most abundant elements in the Earth's crust is used in building construction. When $(A)$ reacts with carbon,it forms a poisonous gas $(B)$,which is a very stable diatomic molecule. Identify compounds $(A)$ and $(B)$.