Question

Which of the following is a Lewis acid but not a Bronsted acid?

• A. $HS{O}_4{}^{-}$
• B. $BC{l}_3$
• C. $N{H}_3$
• D. $HN{O}_3$

Answer 1

Answer: (B)

$BC{l}_3$

Lewis acid is one which accepts lone pair and Lewis base is one which donates lone pair.

Bronsted acid donates $H^{+}$ and Bronsted base accepts $H^{+}$.

$BC{l}_3$ do not have any $H^{+}$ to donate, so it cannot be a Bronsted acid.

But it can accept a lone pair, so it is a Lewis acid, due to empty valence p-orbitals to complete its octet.

Option B is correct.