Which of the following is a specific photosensitive material?

$A$ chemical $A$ is used for the preparation of washing soda to recover ammonia. When $CO_2$ is bubbled through an aqueous solution of $A$,the solution turns milky. It is used in white washing due to its disinfectant nature. What is the chemical formula of $A$?

The following metal ion activates many enzymes,participates in the oxidation of glucose to produce $ATP$,and with $Na^+$,is responsible for the transmission of nerve signals.

Match the following:

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

Alkali metals lose electrons from which orbitals?

Solvay's process is used for the preparation of