Which base among the following reacts with diborane to cleave it unsymmetrically?

Match the following:

List-$I$ (Group $13$ element)	List-$II$ (Metallic radius,$pm$)
$A$. $Al$	$I$. $135$
$B$. $Ga$	$II$. $143$
$C$. $In$	$III$. $170$
$D$. $Tl$	$IV$. $167$

The correct answer is:

The reaction of $H_{3}N_{3}B_{3}Cl_{3}$ $(A)$ with $LiBH_{4}$ in tetrahydrofuran gives inorganic benzene $(B)$. Further,the reaction of $(A)$ with $(C)$ leads to $H_{3}N_{3}B_{3}(Me)_{3}$. Then,compounds $(B)$ and $(C)$ respectively,are

$A$ 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

Boron forms $BX_3$ type of halides. The correct increasing order of Lewis-acid strength of these halides is

Which of the following pairs contains structurally similar substances?