system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:water is h20 , hydrogen peroxide is h202, how can one extra oxygen molecule turn into something that can kill you

title.
gpt
Short answer: because changing even one element in a compound will drastically change how it interacts with other chemicals.

Long answer: H2O is remarkable stable and wants to stay that way. H2O2 is still stable, but it will give the extra oxygen atom to any compound that it can, so it can be more stable. Unlucky for living things, cell membranes will end up taking this extra oxygen and they will no longer be able to hold their form. Once the cell membrane falls apart the cell will die.