How many of the following compounds have one lone pair in central atom? ClF₃, XeO₃, BrF₅, XeF₄, O₃, NH₃

The correct answer is 4.

To determine how many of the given compounds have exactly one lone pair on the central atom, we need to analyze the valence electrons, bonding pairs, and lone pairs for each species:

1. ClF₃ (Chlorine Trifluoride):
The central chlorine (Cl) atom has 7 valence electrons. It forms 3 single bonds with 3 fluorine atoms.
Remaining valence electrons on Cl = 7 - 3 = 4 electrons, which corresponds to 2 lone pairs.

2. XeO₃ (Xenon Trioxide):
The central xenon (Xe) atom has 8 valence electrons. It forms 3 double bonds with 3 oxygen atoms (using 6 electrons).
Remaining valence electrons on Xe = 8 - 6 = 2 electrons, which corresponds to 1 lone pair.

3. BrF₅ (Bromine Pentafluoride):
The central bromine (Br) atom has 7 valence electrons. It forms 5 single bonds with 5 fluorine atoms.
Remaining valence electrons on Br = 7 - 5 = 2 electrons, which corresponds to 1 lone pair.

4. XeF₄ (Xenon Tetrafluoride):
The central xenon (Xe) atom has 8 valence electrons. It forms 4 single bonds with 4 fluorine atoms.
Remaining valence electrons on Xe = 8 - 4 = 4 electrons, which corresponds to 2 lone pairs.

5. O₃ (Ozone):
The central oxygen atom forms 1 single bond and 1 double bond with the terminal oxygen atoms (sharing 3 electrons in bonding).
Taking formal valence allocations, the central oxygen has 6 valence electrons, uses 3 for bonding, and carries a formal charge of +1, leaving 2 non-bonding electrons, which corresponds to 1 lone pair.

6. NH₃ (Ammonia):
The central nitrogen (N) atom has 5 valence electrons. It forms 3 single bonds with 3 hydrogen atoms.
Remaining valence electrons on N = 5 - 3 = 2 electrons, which corresponds to 1 lone pair.

Summary:
The compounds having exactly one lone pair on the central atom are:
1. XeO₃
2. BrF₅
3. O₃
4. NH₃

Thus, there are 4 such compounds.