I think there is a some mistake in the question. Copper is easily dissolved (not Cu(NO3)2) in HNO3 because HNO3 is a strong oxidizing agent than other acids given. It oxidizes the cpooer to copper(II) ion But In presence of HNO3 , copper nitrate is not easily dissolved due to the presence of a common ion NO3- Solution I think there is a some mistake in the question. Copper is easily dissolved (not Cu(NO3)2) in HNO3 because HNO3 is a strong oxidizing agent than other acids given. It oxidizes the cpooer to copper(II) ion But In presence of HNO3 , copper nitrate is not easily dissolved due to the presence of a common ion NO3-.