Which of the following groups would contain the largest number of organisms

The animal kingdom (Animalia)

class (only if the answers are class, order, genus, family)

Explanation depending on the questions answers you'd go by the order of the groups. Domain (1st largest), Kingdom (2nd largest), Phylum (3rd largest), Class (4th largest), Order (5th largest), Family (6th largest), Genus (7th largest), Species (last largest)