Final answer:
According to VSEPR theory, none of the molecules (H2O, CO2, NH3, CH4) have a 90-degree bond angle. CO2 has a linear shape with 180-degree angles, while NH3 and CH4 have angles of approximately 109.5 degrees, and H2O has approximately 104.5-degree angles due to its bent shape.
Step-by-step explanation:
The Valence Shell Electron Pair Repulsion (VSEPR) theory is used to predict the shapes of molecules based on the repulsion between the electron groups on the central atom. When determining which of the molecules (H2O, CO2, NH3, CH4) will have at least one 90-degree bond angle, we consider their molecular geometries.
CO2 has a linear molecular geometry with no 90-degree angles; the molecule is linear as it contains two electron groups (double bonds) around the central carbon atom that repel each other to be as far apart as possible which results in a 180-degree bond angle.
NH3 (ammonia) has a trigonal pyramidal shape and CH4 (methane) has a tetrahedral shape, both with bond angles of approximately 109.5 degrees.
However, in H2O (water), the central oxygen atom has four electron groups: two bonding pairs and two lone pairs, which results in a bent molecular geometry. Due to the presence of lone pairs, which exert a greater repulsive force than bonding pairs, the bond angle is reduced from the tetrahedral angle to approximately 104.5 degrees and there are no 90-degree angles.
Therefore, based on VSEPR theory, none of the molecules or ions listed (H2O, CO2, NH3, CH4) will have a 90-degree bond angle.