For an ideal gas,what is the nature of the $pV$ versus $p$ graph at a constant temperature?

Three bulbs are filled with $CH_4$,$CO_2$,and $Ne$ as shown in the picture. The bulbs are connected through pipes of zero volume. When the stopcocks are opened and the temperature is kept constant throughout,the pressure of the system is found to be $...... \ atm$. (Nearest integer)

Calculate the total pressure in a mixture of $8 \,g$ of dioxygen and $4 \,g$ of dihydrogen confined in a vessel of $1 \,dm^{3}$ at $27^{\circ} C$. $(R = 0.083 \,bar \,dm^{3} \,K^{-1} \,mol^{-1})$

Pressure of $1 \, g$ of an ideal gas $A$ at $27^{\circ} C$ is found to be $2 \, bar$. When $2 \, g$ of another ideal gas $B$ is introduced in the same flask at the same temperature,the pressure becomes $3 \, bar$. Find a relationship between their molecular masses.

At a temperature of $300 \ K$,if the pressure of $0.09 \ mol$ of a gas is halved,what will be its volume?

At $300 \ K$ temperature,the pressure and volume of a gas are $1 \ bar$ and $10 \ L$ respectively. If the pressure becomes $2 \ bar$,calculate the volume of the gas at the same temperature. (in $L$)