Of the following species, which will have bond angles of 120°?

• A. CH_4
• B. BF_3
• C. NH_3
• D. CO_2

Answer: (B)

Verified step by step guidance

1. Identify the molecular geometry of each species by considering the central atom's electron domains (bonding and lone pairs) using VSEPR theory.
2. For \(\mathrm{CH_4}\), the central carbon atom has 4 bonding pairs and no lone pairs, leading to a tetrahedral geometry with bond angles of approximately 109.5°.
3. For \(\mathrm{BF_3}\), the central boron atom has 3 bonding pairs and no lone pairs, resulting in a trigonal planar geometry with bond angles of exactly 120°.
4. For \(\mathrm{NH_3}\), the central nitrogen atom has 3 bonding pairs and 1 lone pair, giving a trigonal pyramidal shape with bond angles slightly less than 109.5° due to lone pair repulsion.
5. For \(\mathrm{CO_2}\), the molecule is linear with 2 double bonds and no lone pairs on the central carbon, so the bond angle is 180°, not 120°.