The correct statement(s) for orthoboric acid is(are)
It is a weak electrolyte
H3BO3+H2O⇌[B(OH)4]−+H+
Clearly, self-ionization is not in play here. The pKa value is 9.25 and this clearly shows that boric acid is a weak electrolyte. Addition of a diol like ethylene glycol and other cis-diols consume the species [B(OH)4]− to drive the above reaction in the forward reaction. When the reaction moves forward, more of H+ is formed and thus the acidity of the system increase.
H3BO3 has a sheet like structure owing to hydrogen bonding. It is not three-dimensional.