The density of a liquid is $1.5 \, g/mL$. There are $50 \, drops$ in $5 \, mL$. The number of molecules in $1 \, drop$ is (molecular weight of liquid is $100$).

If the density of liquid water is $1.0 \, g \cdot cm^{-3}$ and the density of water vapor is $0.0006 \, g \cdot cm^{-3}$ at $100 \, ^\circ C$ and $1 \, atm$ pressure,then what is the volume occupied by water molecules in $1 \, L$ of steam at the same temperature in $cm^3$?

Dinitrogen and dioxygen react with each other to form different compounds. The experimental data is given below:

Mass of Dinitrogen	Mass of Dioxygen
$(i) \ 14 \ g$	$16 \ g$
$(ii) \ 14 \ g$	$32 \ g$
$(iii) \ 28 \ g$	$32 \ g$
$(iv) \ 28 \ g$	$80 \ g$

$(a)$ Which law of chemical combination is followed by the above experimental data? State the law.
$(b)$ Fill in the blanks in the following conversions:
$(i) \ 1 \ km = \dots \ mm = \dots \ pm$
$(ii) \ 1 \ mg = \dots \ kg = \dots \ ng$
$(iii) \ 1 \ mL = \dots \ L = \dots \ dm^3$

$0.05 \ cm$ thick coating of silver is deposited on a plate of $0.05 \ m^2$ area. The number of silver atoms deposited on the plate is . . . . . . $\times 10^{23}$. (Atomic mass of $Ag = 108$,density $d = 7.9 \ g \ cm^{-3}$)

Mole fraction of $O_2$ in an $O_2$ and $O_3$ mixture is $0.25$. Hence,the percentage concentration $\left( \frac{w}{W}\% \right)$ of $O_2$ in the mixture is:

Air contains $23\% \, O_2$ and $77\% \, N_2$ by weight. What is the percentage of $O_2$ by volume?