The covalency and oxidation state respectively of boron in $[BF_4]^-$ are

Which of the following is true for an element in group $13$ of the periodic table?

Identify the correct statement for $B_2H_6$ from those given below.
$(A)$ In $B_2H_6$,all $B-H$ bonds are equivalent.
$(B)$ In $B_2H_6$ there are four $3$-centre-$2$-electron bonds.
$(C)$ $B_2H_6$ is a Lewis acid.
$(D)$ $B_2H_6$ can be synthesized from both $BF_3$ and $NaBH_4$.
$(E)$ $B_2H_6$ is a planar molecule.
Choose the most appropriate answer from the options given below.

The general formula of the compounds formed when group $13$ elements $(A)$ react with group $16$ elements $(B)$ is

The correct statements from the following are:
$(A)$ Ionic radii of trivalent cations of group $13$ elements decrease down the group.
$(B)$ Electronegativity of group $13$ elements decreases down the group.
$(C)$ Among the group $13$ elements,Boron has the highest first ionisation enthalpy.
$(D)$ The trichlorides and triiodides of group $13$ elements are covalent in nature.
Choose the correct answer from the options given below:

The hardest substance amongst the following is