What is the molecular formula of cryolite?

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 - $Al_{2}O_{3}$

In the $Hall-Heroult$ process,which substances are added to alumina to lower its melting point?

When sulfur dioxide gas reacts with hydrogen sulfide gas,sulfur is formed. Which of the following statements about sulfur dioxide is incorrect for this reaction?

Write the electron-dot structure for sodium and chlorine atoms. How do these form a chemical bond? Name the type of bond so formed. Why does a compound so formed have a high melting point?

Name the following:
$(a)$ $A$ metal which is preserved in kerosene.
$(b)$ $A$ lustrous coloured non-metal.
$(c)$ $A$ metal which can melt while kept on palm.
$(d)$ $A$ metal which is a poor conductor of heat.