Which of the following works primarily through oxidation?

The correct answer is iodine. Iodine primarily acts through oxidation, as it is an effective antimicrobial agent due to its ability to oxidize and destroy cell components, such as proteins and nucleic acids, in microorganisms. This oxidative action is instrumental in rendering bacteria and viruses inactive, making iodine a popular choice as a disinfectant and antiseptic in various medical and laboratory settings.

While the other agents listed may also have useful properties in microbial control, they generally do not primarily operate through oxidation like iodine. Alcohols, for example, primarily work through denaturing proteins and dissolving lipids, which impacts cell membranes rather than through direct oxidative interactions. Formaldehyde is a potent chemical often used for its ability to cross-link proteins and nucleic acids, leading to fixation and sterilization but not primarily through oxidation. Chlorine functions as a powerful oxidizing agent as well; however, its primary microbial inactivation mechanism is through the formation of chlorinated compounds and reactive oxygen species that also have oxidizing properties, but unlike iodine, it’s not primarily classified solely under oxidation.

Hence, iodine's predominant mechanism of action through oxidation solidifies its position as the correct answer in this context.