Which of the following species is a Lewis acid (electron-pair acceptor)?

• A. $B_2{H}_6$
• B. $N{H}_3$
• C. $O^2-$
• D. $B_{F_3}$

Answer: (D)

Verified step by step guidance

1. Recall that a Lewis acid is defined as a species that can accept an electron pair, while a Lewis base donates an electron pair.
2. Examine each species to determine if it has an empty orbital or a positive center that can accept electrons:
3. For \(\mathrm{B_2H_6}\) (diborane), it is electron-deficient but generally acts as a Lewis acid due to electron deficiency; however, it is not the best example here compared to \(\mathrm{BF_3}\).
4. For \(\mathrm{NH_3}\) (ammonia), it has a lone pair on nitrogen and tends to donate electrons, making it a Lewis base, not an acid.
5. For \(\mathrm{O_2^-}\) (superoxide ion), it has extra electrons and tends to donate electrons, so it acts as a Lewis base rather than an acid.