If the Admin leaves a WhatsApp group, how is the next Admin chosen? I am in a WhatsApp group. Now, due to some quarrel in the group, the group Admin has left. Now, I have become the Admin of the group all of a sudden.

How is the next Admin chosen? Is it purely random or does the previous Admin choose someone before leaving?
It's purely random

From WhatsApp FAQ 


  If you are the only group admin and you exit a group, a participant is chosen at random to become the new admin


(Emphasis Supplied)