Specify the coordination geometry around and hybridisation of N and B atoms in a 1 : 1 complex of BF₃ and NH₃

Identify the least stable ion amongst the following

Which of the following molecular species has unpaired electrons(s)?

For all complex numbers $${z_1},\,{z_2}$$ satisfying $$\left| {{z_1}} \right| = 12$$ and $$\left| {{z_2} - 3 - 4i} \right| = 5,$$
the minimum value of $$\left| {{z_1} - {z_2}} \right|$$ is