Which of the following are the by-products in the Solvay process for the manufacture of $Na_2CO_3$?

When substance $A$ reacts with water,it produces a combustible gas $B$ and a solution of substance $C$ in water. When another substance $D$ reacts with solution $C$,it produces the same gas $B$,even when reacting with dilute sulfuric acid at room temperature. $A$ gives a golden yellow flame in a Bunsen burner flame. What are $A, B, C,$ and $D$ respectively?

Which of the following sets represents the alkali metals?

Alkali metals are powerful reducing agents because

The dark red colour of bombs in fireworks is due to the presence of:

In the case of alkali metals,the covalent character decreases in the order