Which of the following is considered an antioxidant?

Selenium is recognized as an antioxidant because it plays a crucial role in the body's defense against oxidative stress. Antioxidants are substances that can prevent or slow damage to cells caused by free radicals—unstable molecules that can harm cellular structures. Selenium is a vital component of various antioxidant enzymes, such as glutathione peroxidase, which help neutralize free radicals and thus mitigate potential damage to cells and tissues. Its unique properties allow it to play a protective role in maintaining overall health and preventing chronic diseases associated with oxidative stress.

In contrast, other options do not primarily function as antioxidants. Iron is essential for various bodily processes, including oxygen transport, but excessive iron can contribute to oxidative stress rather than prevent it. Vitamin D is crucial for bone health and immune function but does not have antioxidant properties. Folic acid is vital for DNA synthesis and repair but, similarly to Vitamin D, is not classified as an antioxidant.