The number of species below that have two lone pairs of electrons in their central atom is ___ (Round off to the Nearest integer)
SF$$_4$$, BF$$_4^-$$, ClF$$_3$$, AsF$$_3$$, PCl$$_5$$, BrF$$_5$$, XeF$$_4$$, SF$$_6$$

To find which species have exactly two lone pairs on the central atom, we apply VSEPR theory to each species using the formula: lone pairs $$= \frac{V - B}{2}$$, where $$V$$ is the number of valence electrons on the central atom (adjusted for charge) and $$B$$ is the number of bonding pairs (equal to the number of surrounding atoms in simple cases).

For $$\text{SF}_4$$: sulphur has 6 valence electrons and forms 4 bonds, leaving $$6 - 4 = 2$$ electrons, so 1 lone pair. For $$\text{BF}_4^-$$: boron has 3 + 1 = 4 effective valence electrons and forms 4 bonds, so 0 lone pairs. For $$\text{ClF}_3$$: chlorine has 7 valence electrons and forms 3 bonds, leaving 4 electrons, so 2 lone pairs. This qualifies.

For $$\text{AsF}_3$$: arsenic has 5 valence electrons and forms 3 bonds, leaving 2 electrons, so 1 lone pair. For $$\text{PCl}_5$$: phosphorus has 5 valence electrons and forms 5 bonds, so 0 lone pairs. For $$\text{BrF}_5$$: bromine has 7 valence electrons and forms 5 bonds, leaving 2 electrons, so 1 lone pair.

For $$\text{XeF}_4$$: xenon has 8 valence electrons and forms 4 bonds, leaving 4 electrons, so 2 lone pairs. This qualifies. For $$\text{SF}_6$$: sulphur has 6 valence electrons and forms 6 bonds, so 0 lone pairs.

The species with exactly two lone pairs on the central atom are $$\text{ClF}_3$$ and $$\text{XeF}_4$$, giving a count of $$2$$.