Given below are two statements — Assertion (A) and Reason (R): Assertion (A): NH3 and NF3 molecules have pyramidal…

🧠 In $\mathrm{NH_3}$ the bond dipoles of N–H and the lone pair dipole point in the same direction (both toward N); in $\mathrm{NF_3}$ they point in opposite directions.

🗺️ Evaluate Assertion (A):

• $\mathrm{NH_3}$: μ ≈ 1.47 D; $\mathrm{NF_3}$: μ ≈ 0.24 D
• $\mathrm{NH_3}$ has a greater net dipole moment → A is TRUE ✓

Evaluate Reason (R):

In $\mathrm{NH_3}$: N is the negative end of N–H bonds (N more electronegative than H), and the lone pair also contributes a dipole pointing away from the bond axis — both reinforce each other → large net μ ✓

In $\mathrm{NF_3}$: F is the negative end of N–F bonds, so bond dipoles point away from N; but the lone pair dipole points toward N — they partially cancel → small net μ ✓

R correctly explains A ✓

⚡ The key insight: electronegativity of the attached atoms (H vs F) reverses the direction of bond dipoles relative to the lone pair, drastically changing the net dipole moment.

$\boxed{\text{Answer: Both (A) and (R) are true and (R) is the correct explanation}}$