What is the concentration of water?

One molecule of water has a volume of ........ $\times 10^{-23} \text{ cm}^3$? (Density of water = $1 \text{ g cm}^{-3}$)

If it takes $1$ second to count $4$ grains of wheat,then the time required to count one mole of wheat grains is ...... years.

$A$ sample of $[Cu(NH_3)_4]SO_4$ contains $2.4 \times 10^{24}$ ammonia molecules. The moles of $[Cu(NH_3)_4]SO_4$ in the given sample will be:

Arrange the following in order of increasing mass:
$I$. $1$ mole of $N_2$
$II$. $0.5$ mole of $O_3$
$III$. $3.011 \times 10^{23}$ molecules of $O_2$
$IV$. $0.5$ gram atom of $O$

The number of water molecules present in a drop of water (volume $0.0018 \ mL$) at room temperature is