State the Avogadro hypothesis.

At $0^{\circ}C$,the density of a fixed mass of a gas divided by pressure is $x$. At $100^{\circ}C$,the ratio will be

Oxygen gas is filled in a container of volume $20 \, L$ at a pressure of $2.5 \times 10^5 \, N \, m^{-2}$. Find the mass of the oxygen gas in the container. The temperature of the oxygen in the container is $27 \, ^\circ C$,the molar mass of oxygen is $32 \, g \, mol^{-1}$,and $R = 8.31 \, J \, mol^{-1} K^{-1}$.

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 $B$.

$A$ container of $10 \,L$ is filled with an ideal gas at a temperature of $27^{\circ} C$ at a pressure of $12 \,atm$. The volume of the container is reduced to $6 \,L$ and the temperature of the gas is increased by $30^{\circ} C$. What is the final pressure of the gas (in $\,atm$)?

$A$ certain amount of gas has a volume of $12 \, L$ at a pressure of $3 \, atm$. If the temperature remains constant,what pressure in $atm$ must be applied to reduce its volume to $9 \, L$?