Final answer:
According to the VSEPR theory, the ammonium ion molecule will display tetrahedral molecular geometry.
Step-by-step explanation:
According to the VSEPR theory (Valence Shell Electron Pair Repulsion theory), the ammonium ion (NH4+) molecule will display tetrahedral molecular geometry. This means that the central nitrogen atom is surrounded by four bonding electron pairs, giving it a tetrahedral shape. The molecular geometry of NH4+ is the same as its electron-pair geometry.