Calculate the number of atoms in $0.02$ mole of carbon.

State whether the following statement is true or false:
$A$ mole of any gas always occupies $22.4$ litres of volume at $0^{\circ} C$ and $1$ atmospheric pressure,which is known as standard temperature and pressure $(STP)$.

Give the chemical formulae for the following compounds and compute the ratio by mass of the combining elements in each one of them:
$(a)$ Ammonia
$(b)$ Carbon monoxide
$(c)$ Hydrogen chloride
$(d)$ Aluminium fluoride
$(e)$ Magnesium sulphide

Define mole. Give its symbol. What is the advantage of this mole concept?

Define formula unit mass of a compound. Calculate the formula unit mass of:
$(a)$ $Na_{2}CO_{3} \cdot 10H_{2}O$
$(b)$ $CuSO_{4}$
(Given atomic mass of $Na = 23 \text{ u}, C = 12 \text{ u}, O = 16 \text{ u}, Cu = 63.5 \text{ u}, S = 32 \text{ u}, H = 1 \text{ u}$)

Write the chemical formulae for the following compounds and find the ratio by mass of the combining elements in each one of them.
$(N=14 \ u, H=1 \ u, C=12 \ u, O=16 \ u, S=32 \ u)$
$(a)$ Methane
$(b)$ Carbon dioxide
$(c)$ Hydrogen sulphide