To determine which of the given options is a Brønsted-Lowry acid, we need to understand the definition of a Brønsted-Lowry acid. A Brønsted-Lowry acid is a species that can donate a proton (H⁺).
Let's analyze each option step by step:
A. [tex]\( F^{-} \)[/tex]
[tex]\[ F^{-} \][/tex] is the fluoride ion. It is negatively charged and more likely to accept a proton than to donate one. Therefore, [tex]\( F^{-} \)[/tex] acts as a Brønsted-Lowry base, not a Brønsted-Lowry acid.
B. [tex]\( BF_3 \)[/tex]
[tex]\[ BF_3 \][/tex] is boron trifluoride. It is known to be a Lewis acid because it can accept a pair of electrons due to the empty p-orbital on boron. However, it does not donate a proton, so it does not qualify as a Brønsted-Lowry acid.
C. [tex]\( NH_3 \)[/tex]
[tex]\[ NH_3 \][/tex] is ammonia. Ammonia has a lone pair of electrons on nitrogen and tends to accept a proton to form [tex]\( NH_4^{+} \)[/tex]. Thus, [tex]\( NH_3 \)[/tex] acts as a Brønsted-Lowry base, not as a Brønsted-Lowry acid.
D. [tex]\( NH_4^{+} \)[/tex]
[tex]\[ NH_4^{+} \][/tex] is the ammonium ion. It can donate a proton to revert back to [tex]\( NH_3 \)[/tex]. This ability to donate a proton makes [tex]\( NH_4^{+} \)[/tex] a Brønsted-Lowry acid.
Based on the analysis, the correct answer is:
D. [tex]\( NH_4^{+} \)[/tex]
