Which of the following hydrogen bonds is the strongest?

In which of the following ionization processes, the bond order has increased and the magnetic behaviour has changed?

The charge/size ratio of a cation determines its polarizing power. Which one of the following sequences represents the increasing order of the polarizinig order of the polarizing power of the cationic species, K⁺, Ca²⁺, Mg²⁺, Be²⁺?

Which of the following species exhibits the diamagnetic behaviour?