$Na_2CO_3 + Fe_2O_3 \xrightarrow{\Delta} A + CO_2$. What is $A$ in the reaction?

In the presence of air,washing soda loses $9$ molecules of water to form a monohydrate: $Na_2CO_3 \cdot 10H_2O \xrightarrow{\text{In open air}} Na_2CO_3 \cdot H_2O + 9H_2O$. This process is known as:

Match the following:

Metals	Flame color
$1$. $Li$	$a$. Crimson red
$2$. $K$	$b$. Violet
$3$. $Rb$	$c$. Red-violet
$4$. $Cs$	$d$. Blue

By which method can the concentration of alkali metals be determined?

Which hydride is most stable?

How is magnesium obtained from the following?