Which of the following substances is used in smoke screens?

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 $(B)$.

Explain the following reactions:
$(a)$ Silicon is heated with methyl chloride at high temperature in the presence of copper;
$(b)$ Silicon dioxide is treated with hydrogen fluoride;
$(c)$ $CO$ is heated with $ZnO$;
$(d)$ Hydrated alumina is treated with aqueous $NaOH$ solution.

Which one of the following oxides is expected to exhibit paramagnetic behaviour?

The stability of dihalides of $Si, Ge, Sn$ and $Pb$ increases in the order:

Which of the following products is formed when $SiF_4$ reacts with water?