When manganese oxide (MnO2) from an alkaline battery is mixed with hydrochloric acid (HCl), the expected reaction produces chlorine gas (Cl2) and manganese chloride (MnCl2). Manganese chloride can appear pink in its hydrated form (MnCl2 * 4 H2O). However, the discussion reveals that the observed green substance could be due to a concentrated solution of MnCl2, which may appear green under certain conditions, similar to how concentrated copper(II) salts can change color. There is some confusion regarding the color of chlorine gas, which is typically described as pale yellow-green rather than dark green. The original poster's observation of a green substance remains unclear, as they did not specify whether they were referring to a gas or a solid.
