Which of the following will release hydrogen gas upon reaction with hydrochloric acid?

In the Castner’s process for the extraction of sodium,the anode is made of $.......$ metal.

Fluorosis disease is caused due to the reaction of ...... with excess of fluoride in the body.

Consider the following statements.
$I$. $Cs^{+}$ ion is more highly hydrated than other alkali metal ions.
$II$. Among the alkali metals,only lithium forms a stable nitride by direct combination with nitrogen.
$III$. Among the alkali metals $Li, Na, K, Rb$,the metal $Rb$ has the highest melting point.
$IV$. Among the alkali metals $Li, Na, K, Rb$,only $Li$ forms peroxide when heated with oxygen.
Select the correct statement.

Which among the following is used in the breathing equipment for mountaineers?

Name the industrially important compounds of $Sodium$.