Explanation:

K2NiF6 molecule: It is an ionic compound and consists of two potassium ions, one nickel ion, and six fluoride ions.

Valence electrons: The valence electrons are the electrons present in the outermost shell of an atom. In K2NiF6, the potassium ion has one valence electron, the nickel ion has two valence electrons, and the fluoride ion has seven valence electrons.

Electronic configuration: The electronic configuration of potassium, nickel, and fluoride ions are:

- Potassium ion (K+): 1s2 2s2 2p6 3s2 3p6
- Nickel ion (Ni2+): 1s2 2s2 2p6 3s2 3p6 3d8
- Fluoride ion (F-): 1s2 2s2 2p6

Formation of K2NiF6: When two potassium ions (K+) combine with one nickel ion (Ni2+) and six fluoride ions (F-), the compound K2NiF6 is formed.

Calculation of unpaired electrons: To calculate the number of unpaired electrons in K2NiF6, we need to determine the electronic configuration of the nickel ion in the compound. As per the electronic configuration of Ni2+, there are eight electrons in the d-orbitals.

In K2NiF6, the nickel ion has lost two electrons to form a cation, i.e., Ni2+. Therefore, all the eight electrons in the d-orbitals are paired, and there are no unpaired electrons.

Conclusion: Hence, the number of unpaired electrons in K2NiF6 is zero, as all the electrons in the d-orbitals of the nickel ion are paired.