What gas is produced when the electric stacker is charged, and requires proper ventilation?

When charging an electric stacker, the gas produced that requires proper ventilation is hydrogen. The charging process involves the electrolysis of water in lead-acid batteries, where the chemical reactions can result in the release of hydrogen gas. Hydrogen is highly flammable and poses an explosion risk if allowed to accumulate in enclosed spaces. Therefore, proper ventilation is crucial to disperse any accumulated gas and ensure safety during the charging process.

The other gases listed are either not produced during the charging of electric stackers or do not carry the same risks. Carbon dioxide, while a common gas associated with combustion processes, is not a primary concern with electric stacker battery charging. Oxygen is a byproduct of photosynthesis and not generated in significant amounts during battery charging. Nitrogen, which makes up a large part of the Earth's atmosphere, is inert and does not need special handling in this context. Thus, hydrogen stands out as the gas that specifically necessitates caution and ventilation.