Question

on passing bydrogen gas over the heated black
material Coating on the surface of copper sheets
the black color changes to brown.​

Answer 1

Explanation:

Copper (Cu) when heated in the presence of air turns black. And when Hydrogen gas (H2) is passed over Copper Oxide (Cu2O) the coating of copper which was black will now turn brown again. This is an example of a Redox Reaction.

2Cu + O2 -------> 2CuO

CuO + H2 -------> Cu + H2O