Question

A brownsubstance "X: on heating in air forms substance "Y". When hydrogen gas is passed over heated "Y" it again changes back into "X"
(a) name the subastance X and Y

Answer 1

x is copper , y is copper  oxide
{cu + o2 gives 2cu
and then cuo + h2 gives cu+ h2o}

Answer 2

cu + o2 = 2cu
 cuo + h2 = cu+ h2o
therefore
x is copper , y is copper  oxide