Question

A group $13$ element $X$ reacts with chlorine gas to produce a compound $X{Cl}_3$. $X{Cl}_3$ is electron deficient and easily reacts with ${NH}_3$ to form ${Cl}_{3}X\to {NH}_3$ adduct; however, $X{Cl}_3$ does not dimerize $X$ is:

• A. $B$
• B. $Al$
• C. $Ga$
• D. $In$

Answer 1

The correct option is A $B$

The required 13 group element is Boron.

When it reacts with chlorine then it form $BC{l}_3$

The reaction is as follow:

$2B+3C{l}_2\to 2BC{l}_3$

When it reacts with $N{H}_3$ then it forms adduct which can be represented as $BC{l}_3\leftarrow N{H}_3$ and with excess of ammonia it forms boron nitride.

$BC{l}_3+4N{H}_3\to BN+3N{H}_{4}Cl$

$BC{l}_3$ is electron deficient group but it does not form dimer like $Al,Ga$ or $In$ because its electron deficiency is complemented by the formation of co-ordinate bond between lone pair of electron of chlorine and empty unhybridized p-orbital of boron forming $p\pi -p\pi$ bonding.

Hence, the correct option is $A$.