Question

Assertion :Dipole moment of $N{F}_3$ is less than that of $N{H}_3$ Reason: Polarity of $N-F$ bond is less than that of $N-H$ bond

• A. Assertion is true, Reason is true and Reason is the correct explanation for Assertion
• B. Assertion is true, Reason is true and Reason is NOT the correct explanation for Assertion
• C. Assertion is true, Reason is false
• D. Assertion is false, Reason is true

Answer 1

The correct option is C Assertion is true, Reason is false

$N{H}_3$ has a dipole moment of $1.46D$ and $N{F}_3$ has $0.235D$.
In $N{H}_3$, $H$ is less electronegative than nitrogen and hence, dipole moment of each $N-H$ bond is towards $N$. Now, when we take the vector sum of the three $N-H$ bonds tetrahedrally structured molecule, the dipole moment of the resultant is in the same direction as the dipole created by the nitrogen lone pair. But for $N{F}_3$, as $F$ is more electronegative than $N$, the resultant is opposite to that of lone pair dipole. Hence, reducing the net dipole.