For a monoatomic gas at constant pressure,the $V \rightarrow T$ graph is . . . . . .

Find the approximate number of molecules contained in a vessel of volume $7 \text{ litres}$ at $0^{\circ}C$ and a pressure of $1.3 \times 10^{5} \text{ Pa}$.

Two vessels $A$ and $B$ contain oxygen. The volume of $B$ is twice that of $A$,the pressure of $B$ is thrice that of $A$ and the temperature of $B$ is half of that of $A$. Then,find the ratio of number of molecules of oxygen in vessels $A$ and $B$.

For container $A$,the pressure is $P$,volume is $V$,and temperature is $T$. For container $B$,the pressure is $2P$,volume is $V/4$,and temperature is $2T$. Find the ratio of the number of molecules in container $A$ to that in container $B$.

For three low density gases $A, B, C$,pressure versus temperature graphs are plotted while keeping them at constant volume,as shown in the figure. The temperature corresponding to the point '$K$' is $...........\,{}^{\circ}\,C$.

In the relation $n = \frac{PV}{RT}$,what does $n$ represent?