Which of these about a kingdom is true?

it classifies organisms based on analyzing their genetic links.
it is the most specific category of classification.
the number of domains is more than the number of kingdoms.
it classifies organisms based on broad physical characteristics.

Kingdom classifies organisms based on analyzing their genetic links is the true statement.  

Explanation:

Plantae, Fungi, Animalia, Prokaryote, and Protoctista are six separated kingdoms. With the help of new genetic data now we can easily understand how they are related.  The classification of kingdom is introduced by Robert Whittaker.

Prokaryote: Prokaryote are unicellular and also Microscopic. It is non-membrane bound

Protoctista: It is a small type of eukaryotic organism.  

Plantae, Animalia, Fungi are eukaryotic and also multicellular