In which of the following option/options, the order of arrangement does not agree with the variation of property indicated against it?
(a) \(\text{BF}_3 > \text{NF}_3 > \text{NH}_3\) (Dipole moment)
(b) \(\text{HgCl}_2 > \text{NH}_4^+ > \text{SF}_6\) (Bond angle)
(c) \(\text{NH}_3 < \text{H}_2\text{O} < \text{HF}\) (Strength of intermolecular hydrogen bonding)
(d) \(\text{H}-\text{I} > \text{H}-\text{Br} > \text{H}-\text{Cl}\) (Bond length)

For (a), \(\text{BF}_3\) is a symmetrical trigonal planar molecule, so its dipole moment is zero. Between \(\text{NH}_3\) and \(\text{NF}_3\), \(\text{NH}_3\) has a higher dipole moment because the orbital dipole of the lone pair and the bond dipoles of \(\text{N}-\text{H}\) bonds are in the same direction, whereas in \(\text{NF}_3\), the \(\text{N}-\text{F}\) bond dipoles oppose the orbital dipole. The correct order of dipole moment is \(\text{NH}_3 > \text{NF}_3 > \text{BF}_3\). The given order is incorrect.

For (b), \(\text{HgCl}_2\) is linear with a bond angle of \(180^\circ\), \(\text{NH}_4^+\) is tetrahedral with a bond angle of \(109.5^\circ\), and \(\text{SF}_6\) is octahedral with adjacent bond angles of \(90^\circ\). The correct order of bond angles is \(180^\circ > 109.5^\circ > 90^\circ\). The given order is correct.

For (c), the strength of intermolecular hydrogen bonding depends on the electronegativity of the atom bonded to hydrogen. Since the electronegativity order is \(\text{F} > \text{O} > \text{N}\), the strength of hydrogen bonding follows the order \(\text{HF} > \text{H}_2\text{O} > \text{NH}_3\). The given order is correct.

For (d), the atomic size of halogens increases down the group (\(\text{Cl} < \text{Br} < \text{I}\)). Consequently, the bond length increases in the order \(\text{H}-\text{Cl} < \text{H}-\text{Br} < \text{H}-\text{I}\). The given order is correct.

Therefore, only the arrangement in (a) does not agree with the variation of the indicated property.

Answer: a only