The correct order of atomic radii in group $13$ elements is

Which one of the following is the correct statement?

Given below are the statements about diborane.
$(a)$ Diborane is prepared by the oxidation of $NaBH_{4}$ with $I_{2}$.
$(b)$ Each boron atom is in $sp^{2}$ hybridized state.
$(c)$ Diborane has one bridged $3$ centre$-2-$electron bond.
$(d)$ Diborane is a planar molecule.
The option with correct statement$(s)$ is :

Boron compounds act as Lewis acids due to .....

Which one of the following is the correct statement?

Aluminium $(III)$ chloride forms a dimer because ........