Calculate the number of molecules of sulphur $(S_8)$ present in $16 \, g$ of solid sulphur.

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

What is the mass of :
$(a)$ $0.2$ mole of oxygen atoms?
$(b)$ $0.5$ mole of water molecules?

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

In a reaction,$5.3 \, g$ of sodium carbonate reacted with $6 \, g$ of acetic acid. The products were $2.2 \, g$ of carbon dioxide,$0.9 \, g$ of water,and $8.2 \, g$ of sodium acetate. Show that these observations are in agreement with the law of conservation of mass.
$\text{Sodium carbonate} + \text{Acetic acid} \to \text{Sodium acetate} + \text{Carbon dioxide} + \text{Water}$

What are polyatomic ions? Give examples.