Boric acid is an acid because its molecule

Which of the following sublimes on heating?

$AlF_3$ is soluble in $HF$ only in the presence of $KF$ due to the formation of:

When $AlCl_3 \cdot 6H_2O$ is strongly heated,then it forms

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$ : Boric acid is a weak acid.
Reason $R$ : Boric acid is not able to release $H^{+}$ ion on its own. It receives $OH^{-}$ ion from water and releases $H^{+}$ ion.
In the light of the above statements,choose the most appropriate answer from the options given below.

In the following reaction,assign the state for the underlined atom in the product of complete hydrolysis at $R.T.$:
$H_4\underline{P}_2O_7 + H_2O \longrightarrow 2H_3PO_4$