Question

Which of the following is more polar?

• A. $H_2S$
• B. $NH_3$
• C. $NF_3$
• D. $CHCl_3$

Hint:

A classic chemistry trap compares $NH_3$ and $NF_3$. Even though fluorine is much more electronegative than hydrogen, $NH_3$ is far more polar because its bond dipoles and orbital (lone pair) dipole act in the exact same direction, while in $NF_3$ they act in opposite directions.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Polarity depends on the electronegativity difference between atoms and the molecular geometry (dipole moment vector sum).

Step 2: Formula Application:
Check the direction of the bond dipoles and the lone pair dipole.

Step 3: Explanation:
In $NH_3$, the bond dipoles (N-H) point toward the Nitrogen, which is in the same direction as the lone pair dipole, resulting in a large net dipole moment. In $NF_3$, the bond dipoles (N-F) point away from Nitrogen, partially canceling the lone pair's effect. $NH_3$ has a significantly higher dipole moment than $H_2S$ or $CHCl_3$.

Step 4: Final Answer:
The most polar molecule is $NH_3$.