Asilver article generally turns black when kept in the open for a few days. name
the phenomenon involved. name the black substance formed and give its
chemical formula.

C. chemical changeshope i : )

Idont know. if you want an answer you need to give us some context dude.

Answerδh > 0explanationc₆h₆  (s)  → c₆h₆ (l)if you are changing it from a solid to a liquid, you are pretty much melting the solid. this requires heat energy. therefore, the reaction is endothermic (takes in energy); the system enthalpy increases as the reaction proceeds: δh > 0.