Temperature remaining constant,the pressure of a gas is decreased by $20 \%$. What is the percentage change in volume?

The $P-T$ diagram of an ideal gas having three different densities $\rho_1, \rho_2, \rho_3$ (in three different cases) is shown in the figure. Which of the following is correct?

For an ideal gas,the density of the gas is $\varrho_0$ when temperature and pressure of the gas are $T_0$ and $P_0$ respectively. When the temperature of the gas is $2 T_0$,its pressure becomes $3 P_0$. The new density will be

What is Boltzmann's constant?

An open glass tube is immersed in mercury such that a length of $8 \ cm$ extends above the mercury level. The open end of the tube is then closed and sealed,and the tube is raised vertically by an additional $46 \ cm$. What will be the length of the air column above the mercury in the tube now? (Atmospheric pressure = $76 \ cm$ of $Hg$)

When the pressure on $1200 \ ml$ of a gas is increased from $70 \ cm$ to $120 \ cm$ of mercury at constant temperature,the new volume of the gas will be ........ $ml$.