Final answer:
BF3 is not a Brønsted-Lowry base because it cannot accept a proton due to the absence of an available pair of electrons. NH3, H2O, and PO43− can all act as bases by accepting protons. Therefore, the correct answer is B) BF3.
Step-by-step explanation:
The question concerns the concept of Brønsted-Lowry acids and bases. According to Brønsted-Lowry theory, a base is a substance that can accept a proton (H+), while an acid is one that can donate a proton. When examining the given compounds NH3 (ammonia), BF3 (boron trifluoride), H2O (water), and PO43− (phosphate ion), we are looking for the one that is not a Brønsted-Lowry base.
NH3 is known to accept a proton from water to form NH4+, hence acting as a base. Water (H2O) can also act as a base by accepting a proton to form H3O+. Phosphate ion (PO43−) can accept a proton, forming HPO42−. However, BF3 does not have an available pair of electrons to accept a proton and is, therefore, not considered a Brønsted-Lowry base.
Thus, the correct answer is option B) BF3 as it is not a Brønsted-Lowry base.