The reason for the polymeric nature of boric acid is .....

Sodium borate on reaction with $H_2SO_4$ (conc.) and $C_2H_5OH$ gives a compound '$A$' which burns with a green flame. The compound '$A$' is

$A$ group $13$ element '$X$' reacts with chlorine gas to produce a compound $XCl_3$. $XCl_3$ is electron deficient and easily reacts with $NH_3$ to form $Cl_3X \leftarrow NH_3$ adduct,however,$XCl_3$ does not dimerize. $X$ is

Assertion : Boron is a metalloid.
Reason : Boron shows metallic nature.

Aluminium reacts with dilute $HCl$ and liberates a gas '$A$' and with aqueous alkali liberates a gas '$B$'. $A$ and $B$ respectively are

Given below are two statements: One is labelled as Assertion $A$ and the other is labelled as Reason $R$:
Assertion $A$ : The stability order of $+1$ oxidation state of $Ga$,$In$ and $Tl$ is $Ga < In < Tl$.
Reason $R$ : The inert pair effect stabilizes the lower oxidation state down the group.
In the light of the above statements,choose the correct answer from the options given below :