$A$ 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 $A$?

What is caused by an excess of $Na^+$ in the human body?

Which of the following statement$(s)$ are correct, when alkali metals burn in the presence of oxygen?
$I$. Lithium forms monoxide
$II$. Sodium forms peroxide
$III$. Potassium, rubidium and cesium form superoxide

Match List-$I$ with List-$II$ :

List-$I$	List-$II$
$(a)$ $NaOH$	$(i)$ Acidic
$(b)$ $Be(OH)_{2}$	$(ii)$ Basic
$(c)$ $Ca(OH)_{2}$	$(iii)$ Amphoteric
$(d)$ $B(OH)_{3}$
$(e)$ $Al(OH)_{3}$

Choose the most appropriate answer from the options given below :

Given below are two statements,one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: The alkali metals and their salts impart characteristic colour to reducing flame.
Reason $R$: Alkali metals can be detected using flame tests.
In the light of the above statements,choose the most appropriate answer from the options given below.

The essential constituent of an amalgam is: