The site of calcium, magnesium, iron, and chloride absorption is:

• A. Duodenum
• B. Ileum
• C. Stomach
• D. Jejunum

Answer: (D)

The key idea is where most mineral absorption happens in the small intestine. The jejunum is the major workhorse for absorbing nutrients because it has a vast surface area and abundant transport systems to take up minerals and electrolytes.

For calcium, uptake occurs largely in the proximal small intestine, including the jejunum, via transcellular routes involving TRPV6 channels and calbindin, with additional paracellular passage when calcium is high. Magnesium is absorbed chiefly in the jejunal mucosa through transporters like TRPM6/7. Chloride absorption occurs along the small intestine, with substantial absorption in the jejunum as part of electroneutral NaCl absorption. Iron, while predominantly absorbed in the duodenum, also has uptake in the proximal jejunum via DMT1 and related pathways, so the jejunum participates in iron absorption as food moves beyond the duodenum.

Putting this together, the jejunum best accounts for the absorption of these minerals in a single, common site, since it handles substantial absorption of calcium, magnesium, chloride, and contributes to iron uptake as well.