Calculate the number of molecules in $90$ grams of water.

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 $(STP)$.

One mole of $H_{2}O$ means:
$(i)$ $18 \text{ g}$ of $H_{2}O$
$(ii)$ $6.022 \times 10^{23}$ molecules of $H_{2}O$
$(iii)$ $180 \text{ g}$ of $H_{2}O$
$(iv)$ $1.8 \text{ g}$ of $H_{2}O$

Calculate the number of molecules in $0.5$ mole of water.

$(i)$ Name the body which approves the nomenclature of elements and compounds.
$(ii)$ The symbol of sodium is written as $Na$ and not as $S$. Give reason.
$(iii)$ Name one element which forms diatomic and one which forms tetraatomic molecules.

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