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JEE Advanced 2021 Paper 2 · Chemistry · Chemical Bonding and Molecular Structure · medium

Among the species XeF4, SF4, ICl4^-, BrF3, I3^-, PCl5, SF6, XeF2, XeO3, ClF3, the number of species that possess at least one lone pair on the…

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Among the species XeF4, SF4, ICl4−, BrF3, I3−, PCl5, SF6, XeF2, XeO3, ClF3\mathrm{XeF_4,\ SF_4,\ ICl_4^-,\ BrF_3,\ I_3^-,\ PCl_5,\ SF_6,\ XeF_2,\ XeO_3,\ ClF_3}, the number of species that possess at least one lone pair on the central atom and also have a zero net dipole moment is ______.
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Answer: 4

For each species, find the electron geometry and the shape. XeF4\mathrm{XeF_4} (two lone pairs, square planar) and ICl4−\mathrm{ICl_4^-} (two lone pairs, square planar) have symmetrical vectors that cancel. XeF2\mathrm{XeF_2} and I3−\mathrm{I_3^-} have three equatorial lone pairs and a linear arrangement, so the dipoles cancel. SF4\mathrm{SF_4} (see-saw), BrF3\mathrm{BrF_3} and ClF3\mathrm{ClF_3} (T-shaped) and XeO3\mathrm{XeO_3} (trigonal pyramidal) have lone pairs but a net dipole moment. PCl5\mathrm{PCl_5} (trigonal bipyramidal) and SF6\mathrm{SF_6} (octahedral) are non-polar but have no lone pair on the central atom. Hence four species qualify: XeF4, ICl4−, I3−, XeF2\mathrm{XeF_4,\ ICl_4^-,\ I_3^-,\ XeF_2}.
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