Two chambered heart occurs in

The heart is divided into chambers based on the type of blood it contains, such as oxygenated or deoxygenated blood, and it also has entry and exit points. The hearts of mammals and birds have four chambers: the left atrium, the right atrium, the left ventricle, and the right ventricle. Most reptiles and amphibians have three-chambered hearts with two atriums and one ventricle. The heart is two-chambered, with one atrium and one ventricle to pump blood.

A: Crocodiles- The majority of reptiles have two atria and one ventricle. The only exceptions are the 23 living species of crocodilians (alligators, caimans, crocodiles, and gharials), which have four-chambered hearts with two atria and two ventricles, like birds and mammals.

B: Fish- To pump blood throughout the body, fish have two-chambered hearts, one atrium, and one ventricle. The atrium and ventricle are considered true chambers, while the others are considered accessory chambers. The fish has four compartments. The first is the sinus venosus, which is a sac with thin walls that contains cardiac muscles that collect deoxygenated blood from incoming hepatic and cardinal veins.

C: Aves- The fundamental structures of animal hearts. The hearts of birds and mammals have four chambers (two atria and two ventricles).

D: Amphibians- The heart of an amphibian is three-chambered, with two atria and one ventricle. Because of the timing of the contractions between the atria, the mixing of oxygenated and deoxygenated blood is kept to a minimum.

Hence. The correct answer is B, Fish.