Question

# The number of electron pairs present in the valence shell of a central atom in $S{F_6}$A.4B.6C.8D.7

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Hint:
Any given atom may or may not have multiple oxidation states. This can be determined using the valence electronic configuration and this would in turn help us in finding the number of bonds made.

The central atom in $S{F_6}$ is that of sulphur. We can understand this by looking at the oxidation numbers of the two constituent atoms of the given compound.
The electronic configuration of sulphur is $1{s^2}2{s^2}2{p^6}2{s^2}2{p^4}$. We can see that there are 4 electrons present in the 2p orbital, 2 electrons are present in the 2s orbital. Now, the possible oxidation states for sulphur might occur when,
1.2 electrons are accepted in the incomplete 2p orbital, hence corresponding oxidation state is -2.
2.no electrons are accepted in the 2p orbital, hence corresponding oxidation state is 0.
3.2 electrons are donated from the 2p orbital, hence corresponding oxidation state is +2.
4.4 electrons are donated from the 2p orbital, hence corresponding oxidation state is +4.
5.6 electrons are donated from the incomplete 2s and 2p orbitals, hence corresponding oxidation state is +6.
The corresponding oxidation state for sulphur can be identified by the oxidation state of the atom that is being bonded with sulphur.
In $S{F_6}$, the other element is Fluorine and the electronic configuration of fluorine can be given as $1{s^2}2{s^2}2{p^5}$. Hence, we can see that the valence orbital in Fluorine, i.e. 2p has 5 electrons. It requires just 1 electron to completely fill the 2p orbital. Hence the oxidation state of fluorine is -1, because it accepts one electron to stabilise its valence orbital.
Since there are 6 atoms of fluorine in the given compound, we have 6 electrons with -1 oxidation state attached to only 1 sulphur atom.
Hence the corresponding oxidation state of sulphur in the given compound is +6, thus there are 6 bonds formed between one sulphur and 6 fluorine atoms.
Each bond formed utilises one pair of electrons. Since there are 6 bonds, we can say that the number of electron pairs present in the valence shell of a central atom in $S{F_6}$ is 6 pairs.

Hence, Option B is the correct option.

Note:
It is important to see all the possible oxidation states for elements like sulphur. Because without considering both the oxidation number and the number of other atoms in the compound, the number of bonds formed cannot be accurately determined.