VSEPR Theory Determines Bond Angles in NH4+

Steps:

• Central N atom in NH4+ forms 4 single bonds with H atoms, using all valence electrons.
• Total of 4 bonding pairs and 0 lone pairs on N (steric number 4).
• Electron and molecular geometry both tetrahedral.
• Ideal tetrahedral bond angle is 109.5°, approximated as 107° in given options.

Why B is correct:

• Tetrahedral geometry (AX4) predicts bond angles near 109.5°, with 107° as the closest standard approximation for NH4+.

Why the others are wrong:

• A. 90° applies to square planar geometry (e.g., XeF4).
• C. 105° is typical for bent geometry with lone pair repulsion (e.g., H2O at 104.5°).
• D. 120° occurs in trigonal planar geometry (e.g., BF3).

Final answer: B