What is the meaning of the text on the blackboard?

The text on the blackboard says "Классная работа" which translates to "Classwork" in English. Below that, there is a chemical equation written: HCl + MnO₂ → MnCl₂ + Cl₂ + H₂O. This represents the reaction of hydrochloric acid with manganese dioxide to produce manganese(II) chloride, chlorine gas, and water.