The given sequence represents the reduction of copper oxide $CuO$ to copper sulfate $CuSO4$ through various chemical reactions:

CuO is reduced to Cu $copper$ by losing oxygen.Cu is then treated with hydrochloric acid $HCl$ to form copper chloride $CuCl2$.Copper chloride is further reacted with sodium hydroxide $NaOH$ to produce copper hydroxide $Cu(OH)2$.Finally, copper hydroxide is reacted with sulfuric acid $H2SO4$ to yield copper sulfate $CuSO4$.

This sequence demonstrates the stepwise reduction and modification of copper compounds to ultimately obtain copper sulfate.