JEE MAIN - Chemistry (2025 - 22nd January Evening Shift - No. 9)
$\mathrm{HBr}, \mathrm{H}_2 \mathrm{~S}, \mathrm{NF}_3$ and $\mathrm{CHCl}_3$
Explanation
We need to compare the experimental (or well‐established) dipole moments of the given molecules: $\mathrm{HBr}, \mathrm{H_2S}, \mathrm{NF_3},$ and $\mathrm{CHCl_3}$.
1. $\mathbf{NF_3}$
Structure: Trigonal pyramidal (like $\mathrm{NH_3}$), but each bond is more polar toward fluorine.
Net dipole moment: Quite small, about $0.23\text{–}0.24\,D$ (the bond dipoles partly oppose the lone‐pair contribution).
2. $\mathbf{HBr}$
Structure: Simple diatomic.
Dipole moment: About $0.78\,D$.
3. $\mathbf{H_2S}$
Structure: Bent (like $\mathrm{H_2O}$) but S is less electronegative than O, and the S–H bond angle is wider than the O–H angle in water.
Dipole moment: About $0.95\,D$.
4. $\mathbf{CHCl_3}$ (chloroform)
Structure: Tetrahedral around carbon with three Cl and one H.
Dipole moment: About $1.01\,D$.
Ordering from smallest to largest dipole moment
$ \boxed{\mathrm{NF_3} \;<\; \mathrm{HBr} \;<\; \mathrm{H_2S} \;<\; \mathrm{CHCl_3}.} $
Hence, the correct choice is:
$ \boxed{\text{Option (C)}\quad NF_3 < HBr < H_2S < CHCl_3.} $
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