Deadliest free radical is -

Hydroxyl radicals are generally considered to be the most damaging free radicals. They are considered dangerous because they are extremely reactive. Free radicals are chemical species that have a single unpaired electron in the outer orbit. Most of these are partially reduced reactive oxygen forms that are produced as an unavoidable byproduct of mitochondrial respiration —> also known as reactive oxygen species. The most important are hydrogen peroxide (H2O2), Superoxide anion (O2-) and hydroxyl radical (OH). Free radicals are highly reactive species and toxic -» they can damage the cell membrane and nucleic acids. Free radicals initiate autocatalytic reactions, whereby molecules with which they react are themselves converted into free radicals to propagate the chain of damage. Free radicals are generated by ionizing radiations, metabolism of exogenous chemicals (CCI4) and even during normal metabolic (oxidation-reduction) reactions. Nitric Oxide (NO) may also act as free radical.