Which of the following is a bulk element?

Bulk elements are those that make up a significant portion of living organisms and are essential for biological processes. These elements are typically required in larger quantities compared to trace elements, which are needed in very small amounts.

Calcium is considered a bulk element because it plays crucial roles in various physiological functions, including muscle contraction, neurotransmission, and the formation of bones and teeth. It is found in significant concentrations within the human body, primarily in the skeletal system, and is vital for maintaining structural integrity and signaling pathways.

Iron, while also important for biological systems (especially in oxygen transport via hemoglobin), is classified as a trace element due to the relatively small amounts needed for function. Similarly, chromium is required in even smaller amounts, primarily for glucose metabolism and enhancing insulin action, further categorizing it as a trace element.

Thus, calcium appropriately fits the definition of a bulk element, highlighting its importance and abundance in living organisms.