Final answer:
The sign of cardiac arrest among the provided options is cyanosis (option C). This is because it indicates a lack of oxygen in the blood, which can occur when the heart is no longer pumping effectively during cardiac arrest.
Step-by-step explanation:
The sign of cardiac arrest from the options provided is C. Cyanosis. Cyanosis is a bluish discoloration of the skin resulting from poor circulation or inadequate oxygenation of the blood. Cardiac arrest occurs when the heart fails to pump effectively, leading to a sudden loss of blood flow and lack of oxygen throughout the body.
In contrast, edema is swelling caused by excess fluid trapped in the body's tissues, convulsion is a medical condition where body muscles contract and relax rapidly and repeatedly, and hypertension refers to high blood pressure, which isn't a direct sign of cardiac arrest. Cyanosis can occur in the event of cardiac arrest due to the absence of oxygenated blood circulating in the body.