Final answer:
The bond angle around the central atom in PH₃ is slightly less than 109.5 degrees due to the presence of a trigonal pyramidal molecular geometry and the repulsion caused by the lone pair on the phosphorus atom.
Step-by-step explanation:
The closest bond angle around the central atom in the PH₃ (phosphine) molecule is less than 109.5 degrees. This is because PH₃ has a trigonal pyramidal molecular geometry, similar to NH₃ (ammonia), where there are three hydrogen atoms and one lone pair on the phosphorus atom. The lone pair exerts greater repulsion on the bonding pairs (LP-BP repulsions), resulting in bond angles that are smaller than the ideal tetrahedral angle of 109.5°.
Specifically, in ammonia, the H-N-H bond angle is approximately 107°, and in water, the H-O-H bond angle is about 104.5°. While the exact bond angle for PH₃ is not provided, we can infer that it would similarly be slightly less than 109.5°, due to the lone pair-bonding pair repulsion. Therefore, the correct option would be (B) 109.5 degrees, knowing that the actual angle is slightly less.