Which of the following complex ions does not exist?

$AlCl_3$ on hydrolysis gives:

$BrF_3$ self-ionizes as follows:

Describe the general trends in the following properties of the elements in Groups $13$ and $14$.
$(A)$ Atomic size
$(B)$ Ionization enthalpy
$(C)$ Metallic character
$(D)$ Oxidation states
$(E)$ Nature of halides

In the following reaction $2x + B_2H_6 \rightarrow [BH_2x_2]^+ [BH_4]^-$,$x$ is

In the following reaction,assign the state for the underlined atom for the product of complete hydrolysis at $R.T.$:
$H_4\underline{B}_2O_6 + H_2O \longrightarrow H_3BO_3 + H_2O_2$