JEE Main · 2024 · 30 Jan 2024 · Shift 2 · Chemical Bonding and Molecular Structure

In ${\text{NH}}_3$, the lone pair on nitrogen and the three polar N–H bonds (bond dipole pointing towards the more electronegative N) both act in roughly the same direction, so they reinforce, giving a resultant dipole moment of about 1.46 D. In ${\text{NF}}_3$, the N–F bond dipoles point from N towards the more electronegative F, i.e. away from nitrogen, opposing the lone-pair dipole that still points away from the N–F bonding density towards N; the two largely cancel, so ${\text{NF}}_3$ has a much smaller net dipole moment (about 0.24 D) than ${\text{NH}}_3$ — Statement I is false. Statement II reverses this: it claims the lone pair and bond dipoles oppose in ${\text{NH}}_3$ and reinforce in ${\text{NF}}_3$, the opposite of the actual situation, so it is also false. Both statements are false.