1. When adding strong base to a buffer, why can we assume the equilibrium value of the OH- is zero?

When adding strong base to a buffer, we assume the equilibrium value of the hydroxyl ion (OH-) is zero because all hydroxyl ion (OH) react with hydrogen ion (H+) forming water. So there is no hydroxyl ion (OH-) left and values of hydroxyl ion (OH-) is become zero.

Hydrogen ion is released by weak acid which is present in the buffer solution.

the electronic configuration of an atom with eight electrons is 1s²2s²2p⁴. the orbital diagrams are shown in the figure.

as per the hunds rule:

1. electrons tend to avoid being in the same orbital as per as practicable.

2. electrons in different orbitals of the same energy will have their spin parallel.

this can be illustrated from the multiplicity of the orbitals of the atom. as there are four electrons in the p orbital and p orbital has 3 sub-shells. the electrons can be fed in different ways as shown in the figure but the correct orbital diagram will be as per the hunds rule.