Which of the following has the lowest bond angle? 

CONCEPT:

Bond Angle

• The bond angle is determined by the repulsion between bonding pairs and lone pairs of electrons around the central atom, as described by the VSEPR (Valence Shell Electron Pair Repulsion) theory.
• The presence of lone pairs reduces bond angles as they exert greater repulsion compared to bonding pairs.
• Bond angles are largest in symmetrical molecules with only bonding pairs (e.g., tetrahedral molecules like CH₄) and decrease as lone pairs are introduced.

EXPLANATION:

• NH₃: Ammonia has a trigonal pyramidal shape with one lone pair on the nitrogen atom. The lone pair-bond pair repulsion reduces the bond angle from the ideal tetrahedral value of 109.5° to approximately 107°.
  
• NH₄⁺: The ammonium ion has a perfect tetrahedral geometry with no lone pairs on the central nitrogen atom. The bond angle is 109.5°.
• CH₄: Methane also has a tetrahedral geometry with no lone pairs on the central carbon atom. The bond angle is 109.5°.
  
• Since NH₃ has one lone pair, the lone pair-bond pair repulsion reduces its bond angle to 107°, making it the lowest among the options provided.
• NH₂^-
• 

Therefore, the molecule with the lowest bond angle is NH2-, and the correct answer is Option 3.