What is meant by the term chemical formula?

Write down the names of compounds represented by the following formulae:
$(i) Al_{2}(SO_{4})_{3}$
$(ii) CaCl_{2}$
$(iii) K_{2}SO_{4}$
$(iv) KNO_{3}$
$(v) CaCO_{3}$

Calculate the number of aluminium ions present in $0.051 \, g$ of aluminium oxide.
[Hint: The mass of an ion is the same as that of an atom of the same element. Atomic mass of $Al = 27 \, u$.]

When $3.00 \,g$ of carbon is burnt in $8.00 \,g$ of oxygen,$11.00 \,g$ of carbon dioxide is produced. What mass of carbon dioxide will be formed when $3.00 \,g$ of carbon is burnt in $50.00 \,g$ of oxygen? Which law of chemical combination will govern your answer?

Convert the following into moles:
$(a)$ $12\, g$ of oxygen gas
$(b)$ $20\, g$ of water
$(c)$ $22\, g$ of carbon dioxide.

Hydrogen and oxygen combine in the ratio of $1:8$ by mass to form water. What mass of oxygen gas would be required to react completely with $3 \,g$ of hydrogen gas (in $,g$)?