Question

A brown substance ‘X' on heating in air forms a substance ‘Y'. When hydrogen gas is passed over it again back into ‘X. Name types of chemical reaction occuring during both the changes and write the chemical equations

Answer 1

X element is copper and Y is copper oxide.
oxidation and redox reaction is taking place in the first and second reaction.

on heating in air:-
2Cu + O2 -------> 2CuO
When hydrogen gas is passed over black copper oxide then it turns brown as oxygen is removed by hydrogen:-
2CuO + H2 ------> Cu + H2O

hope it helps:)