VSEPR theory determines bond angles via electron pair repulsions

Steps:

• Identify central atom and electron domains (bonding + lone pairs) for each.
• Predict geometry: tetrahedral (AX4) for 109.5°; trigonal pyramidal (AX3E) for ~107°; bent (AX2E2) for ~111°.
• Calculate/comparison: lone pairs compress bond angles below ideal tetrahedral.
• Select option with lone pair repulsion causing smallest angle.

Why C is correct:

• NH3 has AX3E geometry; lone pair repels bonds more than bond pairs, reducing H-N-H angle to 107° per VSEPR.

Why the others are wrong:

• A. CH4 is AX4 tetrahedral with ideal 109.5° angle, no lone pairs.
• B. CH3OCH3 has AX2E2 bent O geometry with C-O-C angle ~111°, larger due to weaker lone pair effects.
• D. NH4+ is AX4 tetrahedral with 109.5° angle, no lone pairs to compress.

Final answer: C