Final answer:
The right atrium of the heart is the chamber that receives deoxygenated blood from the body via the vena cava. Therefore, the correct option is B.
Step-by-step explanation:
The cavity in the heart that receives deoxygenated blood from the body is the right atrium. The deoxygenated blood enters the right atrium through the vena cava, which is a large vein that carries the blood from the body back to the heart. After the blood fills the right atrium, it then moves to the right ventricle through the tricuspid valve, which then pumps it to the lungs for oxygenation via the pulmonary artery. Therefore, the correct answer to the question is B. Right atrium.