Which of the following is a compound of hydrogen and oxygen?

What is formed when boiling sulfur reacts with dihydrogen gas?

Why should metal sulphides and carbonates be converted to metal oxides during the process of metal extraction?

$(a)$ Carbon cannot be used as a reducing agent to obtain $Mg$ from $MgO$. Why?
$(b)$ How is sodium obtained from molten sodium chloride? Give the equations of the reactions.
$(c)$ How is copper obtained from its sulphide ore? Give the equations of the reactions.

Why is hydrogen gas not evolved when a metal reacts with nitric acid?

Who discovered hydrogen gas?