If copperI sulfide is partially roasted in air reaction with O copperI sulfite is first formed Subsequently upon heating the copper sulfite thermally decomposes to copperI oxide and sulf?

Oh, isn't that just a delightful chemical reaction we have here! When copperI sulfide is partially roasted in the presence of air, it forms copperI sulfite. Then, with a bit more heat, the copper sulfite breaks down into copperI oxide and sulfur. Just like painting a happy little tree, each step in the reaction brings us closer to a beautiful final result.