$$\_\_\text{Cu}+\_\_\text{H2SO4(conc.)}\stackrel{\text{calor}}{\to }$$

$$\_\_\text{Cu}+\_\_\text{HNO3(conc.)}\to$$

$$\_\_\text{Na2S2O3(aq.)}+\_\_\text{I2(aq.)}\to$$

$$\_\_\text{FeS2}+\_\_\text{O2}\stackrel{\text{5000∘C}}{\to }$$