Question

___________ [greenish yellow/reddish brown] gas is evolved when conc. Hydrochloric acid is heated with manganese dioxide.

Answer 1

A greenish-yellow gas is evolved when conc. Hydrochloric acid is heated with manganese dioxide.

1. When concentrated hydrochloric acid reacts with manganese dioxide, it produces greenish-yellow chlorine gas, as well as manganese$\left(II\right)$ chloride and water.
2. Hydrochloric acid works as a reducing agent, whereas manganese dioxide functions as an oxidizing agent in this process. It produces chlorine gas by oxidizing hydrochloric acid