Which of the following is added to borax to obtain boric acid?

Which of the following chlorides does not react with $PCl_5$ on heating?

Given below are two statements :
Statement $I$ : Gallium is used in the manufacturing of thermometers.
Statement $II$ : $A$ thermometer containing gallium is useful for measuring the freezing point $(256 \ K)$ of brine solution.
In the light of the above statement,choose the correct answer from the options given below :

Consider the following reactions (not balanced):
$BF_3 + NaH \xrightarrow{450 \ K} X + NaF$
$X + H_2O \longrightarrow Y + H_2 \uparrow$
The correct statements about $X$ and $Y$ are:
$I$. $X$ is an electron-deficient molecule
$II$. In $X$, $B-B$ bond is present
$III$. $Y$ is a weak tribasic acid
$IV$. $Y$ acts as a Lewis acid

Which of the following is true for an element in group $13$ of the periodic table?

Conc. $HNO_3$ can be stored in a container of