$BCl_3$ does not exist as dimer but $BH_3$ exist as dimer $(B_2H_6)$ becuase
Chlorine is more electronegative than hydrogen
There is $p\pi -p \pi $ back bonding in $BCl_3$ but does not contain such multiple bonding
Large sized chlorine atoms do not fit in between the small boron atoms whereas small sized hydrogenatoms get fitted between boron atoms
none of these
Assertion : Boron is metalloid.
Reason : Boron shows metallic nature.
Correct match is :
Explain the nature of boric acid as a Lewis acid in water.
Discuss the pattern of variation in the oxidation states of
$(i)$ $B$ to $Tl$ and $(ii)$ $C$ to $Pb$.
Borax on heating strongly above its melting point melts to a liquid, then solidifies to a transparent mass commonly known as Borax Bead. The transparent glassy mass consists of :