Which one of the following is the correct statement?

(i) It is a weak monobasic acid soluble in water and in aqueous solution boron atom completes its octet by accepting $\mathrm{O}{\mathrm{H}}^{–}$ from water molecules:
$\mathrm{B}{\left(\mathrm{O}\mathrm{H}\right)}_3+2{\mathrm{H}}_2\mathrm{O}\to {\left[\mathrm{B}{\left(\mathrm{O}\mathrm{H}\right)}_4\right]}^{-}+\mathrm{ }{\mathrm{H}}_3{\mathrm{O}}^{+}$
(ii) Only $\mathrm{T}{\mathrm{l}}^{3+}$ acts as an oxidising agent on account of inert pair effect.
(iii) In the solid state, the $\mathrm{B}{\left(\mathrm{O}\mathrm{H}\right)}_3$ units are hydrogen bonded together into two dimensional
sheets with almost hexagonal symmetry.

(iv) $\mathrm{B}{\left(\mathrm{O}\mathrm{E}\mathrm{t}\right)}_3$ imparts green colour to the burner flame.