Which of the following are cations in the body?

In the context of human physiology, cations are positively charged ions that play crucial roles in various bodily functions, including maintaining fluid balance, transmitting nerve impulses, and muscle contractions. Sodium and calcium are both essential cations in the body.

Sodium is the primary cation in extracellular fluid and is vital for maintaining osmotic pressure and fluid balance, as well as playing a key role in action potentials for nerve conduction. Calcium, found primarily in the bones, is crucial not only for structural support but also for muscle contraction, blood coagulation, and neurotransmitter release.

The other options include ions that are not classified as cations. Chloride and phosphate, for example, are anions, meaning they carry a negative charge. Bicarbonate, despite being involved in buffering systems, also carries a negative charge, making it an anion as well. Hence, the presence of sodium and calcium as cations highlights the importance of these ions in physiological processes, establishing them as the correct choice in this context.