How many carats is pure gold?

Four groups are given linking a metal, its ore, and the chemical formula of the main component of the ore. How many of these are correct?
$(1)$ Iron - Magnetite - $Fe_{3}O_{4}$
$(2)$ Iron - Siderite - $FeS_{2}$
$(3)$ Copper - Copper glance - $Cu_{2}S$
$(4)$ Copper - Dolomite - $Al_{2}O_{3}$

Which method is used to collect $H_2$ gas in a gas jar in the laboratory?

Which gas has a pungent smell that causes choking and coughing?

What happens when a glass rod dipped in concentrated hydrochloric acid is brought near a container filled with ammonia gas?

What is the number of electrons lost by a metal atom to form a positive ion called?