Which is the strongest Lewis base?

• A. SbH₃
• B. AsH₃
• C. PH₃
• D. NH₃

The strength of a Lewis base is determined by its ability to donate an electron pair. Among the options provided, the strongest Lewis base is typically NH₃ (ammonia). This is due to its nitrogen atom, which has a lone pair of electrons that can readily be donated to form a bond with a Lewis acid.

Comparison of the Options

• SbH₃ (stibine): While it has lone pairs, it is less basic due to the larger size and lower electronegativity of antimony.
• AsH₃ (arsine): Similar to stibine, it is a weaker base compared to ammonia because arsenic is also larger and less electronegative.
• PH₃ (phosphine): This compound is even less basic than ammonia, as phosphorus is larger and less effective at donating its lone pair.
• NH₃ (ammonia): It has a strong tendency to donate its lone pair, making it the strongest Lewis base among the choices.

In summary, when comparing these compounds, NH₃ stands out as the strongest Lewis base due to its favorable electron-donating properties.