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 $OH^{–}$ from water molecules:
$B{\left(OH\right)}_{3} + 2{H}_{2}O \to {\left[B{\left(OH\right)}_{4}\right]}^{-} + {H}_{3}O^{+}$
(ii) Only $Tl^{3 +}$ acts as an oxidising agent on account of inert pair effect.
(iii) In the solid state, the $B{\left(OH\right)}_{3}$ units are hydrogen bonded together into two dimensional
sheets with almost hexagonal symmetry.

(iv) B{\left(OEt\right)}_{3} imparts green colour to the burner flame.